问题
选择题
Although the police thought he was the most likely one, _____ they had no exact proof about it, they could not arrest him.
A．when
B．until
C．before
D．since
答案
答案：D
考查连词. A.当……时候B.直到…… C.在……以前 D.因为；由于；自……以来。句意：尽管警察认为他是最可能的一个，由于他们没有确切的证据，他们也不能逮捕他。选D。