1). Because is a conjunction, used at the beginning of a clause, before a subject and a verb.
We were late because it rained.
I'm happy because I met you.
2). Because of is a two - word preposition used before a noun or a pronoun.
We were late because of the rain.
I'm happy because of you.
Note: "Because" and its clause can go after or before the main clause.
I finished early because I worked fast.
Because I worked fast, I finished early.
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