单选题 We ______ on this project for four hours. Let's have a rest.
A. are working B. have been working
C. worked D. had worked

【正确答案】 B
【答案解析】[解析] 本题考查动词的时态，由“four hours”可知应用完成时态，排除A和C：由“Let's have a rest”可知工作还没完，因此应该用现在完成进行时。故选B。