the police thought he was the most likely one since they had no exact proof about it the

问题补充：

the police thought he was the most likely one, since they had no exact proof about it,they had to set him free.

A. As long as

B. If only

C. Although

D. As though

答案：

A. As long as

B. If only

(答案→)C. Although

D. As though

解析：连词辨析。A只要；B要是…就好了；C尽管，即使；D似乎，好像；句意：尽管警察认为他是最有可能的一个，但是因为他们没有确切的证据，他们不得不把他释放了。故C正确。