Participles

A participle is a verbal (verb form) which is used as an adjective.

There are three participles that are commonly used as adjective: the present participle(active voice); the past participle (passive voice) and the perfect participle (active voice).

* The present participle always ends in ing
* The past participle usually ends in ed, d, t, n, or en.The past participle of some of the verbs do not have distinctive endings: swum, gone, sung etc.
*The perfect participle is always formed by prefixing the word having to the past participle: having sung, having driven, having seen etc

Consider an example from GMAT Prep SC:

First discovered more than 30 years ago, Lina's sunbird, a four-and-a-half-inch animal found in the Phillippines and that resembles hummingbird, has shimmering metallic colors on its head; a brilliant orange patch, bordered with red tufts, in the center of its breast; and a red eye.

A. found in the Phillippines and that resembles
B. found in the Phillippines and that, resembling
C. found in the Phillippines and resembling
D. that is found in the Phillippines and it resembles
E. that is found in the Phillippines and that, resembling

OA : C

As we know :

Past participle ---- represents
1) a past condition, or
2) the passive voice or
3) a condition done onto the subject

Present participle ---- represents
1) a present condition, or
2) the active voice or
3) a condition performed by the subject

In the given sentence, we can clearly see that for the 1st participial phrase, the action of "found" happened in the past because Lina's sunbird was found more than 30 years ago. Further Lina's sunbird did not do any finding instead they were found by X not mentioned in the sentence so passive voice is right.

The second participial phrase starting with "resembling" implies that the "Lina's sunbird" is still resembling in the present(a present condition), so the use of present participle is better. We cannot say that the Lina's sunbird "resembled" because then this would illogically mean that they no longer resemble the humming bird.

The present and past participles are used to describe the "Lina's sunbird", they act as adjectives..

For more examples click on the link below:
GMAT Sentence Correction Questions

Until vs. As long as

Until can be used both as a preposition and as a conjunction. Until is used to express a point of time in the future

Until (preposition) -

1. Up to the time of: We danced until dawn.
2. Before (a specified time): She can't leave until Friday

Until (conjunction) -

1. Up to the time that: We walked until it got dark.
2. Before: You cannot leave until your work is finished.
3. To the point or extent that: I talked until I was hoarse

As long as means that one thing will occur while another thing is still true

As long as (conjunction) -

1. During the time that: I'll stay as long as you need me.
2. Since: As long as you've offered, I accept.
3. On the condition that: I will cooperate as long as I am notified on time.

Idiom

1. For the period of time that, as in You may keep the book as long as you want, that is, keep it for whatever time you wish to.
2. Also, so long as. Since, because, as in Please pick up some milk as long as you are going to the store, or So long as you're here, you might as well stay for dinner.
3. Also, so long as; just so. Provided that, as in As long as you don't expect it by tomorrow, I'll make the drawing, or So long as sales are greater than returns, the company will make a profit, or You may have another cookie, just so you don't take the last one.

Source: http://www.answers.com

1. In order to express a future idea. after as long as, we use a present tense.
e.g - As long as I live, I shall smoke no more cigarettes
2. Before a number, as long as can be used to suggest great length
e.g - The discussion can last as long as six hours

Verb, Infinitive, Gerund - 1

Below is the list of Verbs generally followed by an infinitive with to

agree
appear - e.g Her health appeared to be worse
arrange
ask
attempt
care
claim
dare
decide - e.g We decided to go to Hawaii
demand
deserve
endeavor
expect
fail
get
grow
happen
hasten
help
hesitate
hope
hurry
intend
leap
learn
long
make (passive)
manage
neglect
offer
pay
plan - e.g We plan to go to India this year
pledge
pretend
refuse - e.g: I refuse(verb) to lie(infinitive) to my friends
resolve
say
seek
seem
struggle
swear
tend
vow
want
would like - e.g We would like to leave now
wish
yearn

Verbs + infinitive with to or a gerund:

attempt
begin - e.g He began singing; He began to sing
can't bear
continue
dread - e.g She dreaded taking the risk; She dreaded to think of the consequences of her actions
forget
go on
hate
intend
love - e.g She loves to dance; She loves dancing
mean
plan
prefer
propose
regret
remember
start
stop - e.g He stopped drinking; He stopped to rest for a few minutes
try

Verbs + object + infinitive with to or a gerund

admit
allow
consider
forbid
imagine
keep(in order to) - e.g The attackers kept hostages to prevent the police from entering; She kept talking.
need - e.g He need to call his boss; The house needs cleaning
permit
require

Usage of One

In sentences that contain the phrase one of.....

1. In simple form one of or one of the, a singular verb is used.

e.g - One of the books is missing from my cupboard.

2. In sentences that contain phrases one of those who or one of the things that, a plural verb is used.

e.g - He is one of our employees who are always alert.

3. When only precedes one of /one of those, a singular verb is used. (Do not mix this rule with the 2nd rule stated above)

e.g - Ram is the only one of our employees who is always alert.

Aim to vs Aim at

Aim to (idiom)

Try or intend to do something.

• We aim to please our customers.
• She aims to fly to California.

Correct usage: aim to + verb

Aim at (idiom)

Direct a missile or criticism at something or someone.

• In his last speech the President took aim at the opposition leader.
• He aims at finishing tomorrow.

Correct usage: aim at + noun

Different from vs Different than

Different from means not the same.

e.g. Sara's taste is different from mine.

Different than: In US English, than is an alternative to from before a clause.

e.g. Sara's appearance was very different than I'd expected.

NOTE : On GMAT different than is always wrong when comparing two nouns. 
Different than is only correct when a sentence compares a noun and a clause.


On GMAT sentence correction if you come across a question comparing two nouns and a choice with the phrase different than eliminate that choice.
Since the 18th century, language critics have singled out different than as incorrect.

Editing Comma Splice

Comma splice is the error of joining two independent clauses with nothing but a comma.

Comma splice has two main forms -

1). Run on sentence joined by a comma alone. (Run on sentences are independent clauses that have not been joined correctly).

e.g - Some gourmets like the new French cooking, others find it dull. - incorrect - comma splice run-on.

2). Run on sentence joined by a comma and a word that is not a coordinating conjunction.

e.g - Some gourmets like the new French cooking, however, others find it dull. - incorrect - comma splice run-on.

There are 4 ways to revise a run on sentence.

1). Use a comma and a coordinating conjunction.

e.g - Some gourmets like the new French cooking, but others find it dull. - Correct

2). Make the clauses into seperate sentences.

e.g - Some gourmets like the new French cooking. Others find it dull. - Correct

3). Restructure the sentence i.e convert an independent clause to subordinate/dependent clause.

e.g - Although some gourmets like the new French cooking, others find it dull. - Correct

4). Use a semicolon.

e.g -

Some gourmets like the new French cooking; others find it dull. - Correct

OR

Some gourmets like the new French cooking; however, others find it dull. - Correct.

OG 10th - Ques number 10 - Example of Comma splice run-on.

10. However much United States voters may agree that there is waste in government and that the government as a whole spends beyond its means, it is difficult to find broad support for a movement toward a minimal state.

(A) However much United States voters may agree that
(E) There is agreement among United States voters that

A is the correct answer.

E - incorrect

E starts with an independent rather than a subordinate clause i.e
(There is agreement among United States voters that there is waste in
government and that the government as a whole spends beyond its means)

and

separates its two independent clauses with a comma hence creates a run-on sentence.
There is agreement among United States voters that there is waste in government and that the government as a whole spends beyond its means -- Independent clause
It is difficult to find broad support for a movement toward a minimal state. -- Independent clause