He ______ in the factory for three years before he joined the army.

He ______ in the factory for three years before he joined the army.
A. has worked B. has been working C. had worked D. worked
【答案】C
【解析】
【详解】考查时态。句意：他参军前已经在该工厂工作了三年。分析句子可知，设空处是主句谓语动词，且“工作”发生在“参军”之前，即过去的过去，应用过去完成时had done。故选C项。