【题目】Don't call me at the office ________ it is necessary.
A.before
B.unless
C.although
D.till

【答案】B
【解析】考查连词。句意：请不要打电话到我的办公室，除非是真的有必要。A. before在……以前；B．unless除非，引导条件状语从句；C. although尽管；D. till直到……为止。故选B。