Which of the following is a dependent clause?

because they went to school

Jessica rides her bike every day

yesterday Luca tried out for the soccer team

I will see you later

The answer is a, "Because they went to school."

This is because that statement does not give information on what happened due to them going to school. If you were to leave out "Because" surely it would stand alone as a sentence, given enough context.

I think the answer is A

A dependent clause is a group of words with a subject and a verb. It does not express a complete thought so it is not a sentence and can't stand alone.