问题
选择题
The workers _____busily when the boss came to look for something she ______in the office.
A had worked, had left B were working ; had left C working ; had left D had worked; left
答案
答案：B
前一空表示当时正在进行的动作，所以用过去进行时，第二空用过去进行时表示这动作在came之前。