در تست زیر گزینه a صحیح تر است یا گزینه c ؟

اشتراک گذاری در شبکه های اجتماعی

Police have released further details about the accident …………..they were forced to.
a. when
b. as
c. since
d. while

The same answer. It seems that it is to check the concept of "since" here. "As" is also possible meaning "because".