Which provides the PRIMARY function of the underlined adverbial clause?

Because Brady loved Willow, he refused to believe that she had deserted him.

*Concession is a thing that is granted, especially in response to demands.
Responses
A adverbial clause of timeadverbial clause of time
B adverbial clause of reasonadverbial clause of reason
C adverbial clause of *concessionadverbial clause of *concession
D adverbial clause of manner or condition