题目

The students _______ busily when Miss Brown went to get a book she _______ in the office. A. had written, left          B. were writing, has left C. had written, had left  D. were writing, had left 答案：D 解析: “把书忘在办公室”发生在“去取书”这一过去的动作之前，因此“忘了书”这一动作发生在过去的过去，用过去完成时。句中when表示的是时间的一点，表示在“同学们正忙于……”这一背景下，when所引导的动作发生。因此前一句应用过去进行时。18．320mL=0.32L2340L=2.34m30.5m3=500dm3．