【题目】Our capital, Beijing, ______ on improving the city’s environment in the past three years through various measures.
A. has been workingB. were working
C. workedD. had worked
在线课程【答案】A
【解析】
考查动词时态。句意：在过去的三年里，我们的首都北京通过各种措施致力于改善城市环境。由下文“in the past three years”可知，在过去的三年里北京一直致力于改善环境，动作具有延续性，所以应该用现在完成进行时。故选A。