单选题 ______ something drastic happens before midnight, the postal workers will most likely walk out on their jobs.

【正确答案】 C
【答案解析】something drastic happens before midnight是完整的结构，所以横线处应填入引导状语从句的从属连词。备选答素中只有(C)unless是从属连词，不用分析全句，也可以轻松找到答案。