从每小题的A、B、C、D四个选项中，选出可以填入空白处的最佳选项，并在答题卡上将该选项涂黑。
11. This suitcase looks heavy but actually ________ is very light.
A. that B. this C. it D. one
12. They will fly to Beijing, ________ they plan to stay for two or three days.
A. which B. where C. there D. when
13. Wouldn’t it be nice if students had to go to ________ school only four days ________ week?
A. 不填; a B. 不填; the C. the; a D. the; the
