单选题 We ______ on it for many hours, but we have not yet reached any conclusion.
A. are being worked B. are working
C. have been working D. have been worked

【正确答案】 C

【答案解析】[解析] 考查知识点：现在完成进行时的用法。从时间状语“for many hours”可以看出，谓语动词应该用现在完成进行时。