When are colons used? Select three options. A colon separates clauses in a series.
A colon signals that a list follows.
A colon appears in 12-hour time notations.
Acolon is used after an introductory phrase.
A colon follows the greeting in a formal letter.

Colons are used in the following:

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A dependent clause is a clause that needs a beginning or an end to support it. In this example, "before he returns to work" would be the dependent clause.

Explanation:

This dependent clause tells us when he wants to visit his friends. If you were to write a sentence that just says "before he returns to work," it would not be complete. The sentence, "Allen wants to visit his friends," sounds complete, so it is independent.