动词适当形式填空
1. When we arrived at the park ,Lily__(leave).
2.I ___(finish) the exercise in few hours.
3.Their luggage ___(check)as they entered the building.
参考答案:1,had left
leave发生在arrived（过去）的过去
2，will finish
3，was being checked
在他们进入时正在被检查,as为动作同步的标志