II. 单项选择（共15小题；每小题1分，满分15分）
从A、B、C、D四个选项中，选出可以填入空白处的最佳选项，并在答题卡上将该项涂黑。
21. I will never forget ____ to country village to see the poor children of my age.
A. to take B. to be taken C. taking D. being taken
22. He was about to go out for a walk _____ his teacher came to visit him.
A. while B. which C. when D. then
