The police set about arresting the suspect ______ they found enough evidence to prove him guilty.

c
因为the moment可作连词用,意为“一……就”.根据意思,警察一发现足够证明嫌疑犯有罪的证据,就会着手逮捕他.
a的话,一般用immediately表达“一……就……”,如
I'll give you an answer immediately I've finished
reading your file.我读完你的卷宗以后立即给你答复.
bd的话,解释为“只要……就”
那么其实还是回归到语文问题上,这里填条件状语从句“只要……就”还是“一……就”,哪个好,不言而喻那么BD在语法结构上有问题吗？