单选题 ______ something drastic happens before midnight, the postal workers will most likely walk out on their jobs.
A. Also B. Except C. Unless D. Therefore

【正确答案】 C
【答案解析】[解析] 横线后的内容是完整的句子结构，所以横线处应填入引导状语从句的从属连词。备选答案中只有(C)unless是从属连词，故选C。