The correct answer is adverbial clause.
An adverbial ( adverb ) clause is a group of words that function as an adverb in a sentence.
Adverb clauses add information that elaborates on when, where, why, how the action in the sentence takes place.
An adverb clause must contain a subject and a verb to be complete.
An adverb clause can be used at the beginning of a sentence:
Before you do your homework, go and see your sister.
They can also be placed at the end of a sentence:
The day felt lonely because nobody came to visit me.
