请认真阅读下面各题，从题中所给的A、B、C、D四个选项中，选出最佳选项，并在答题卡上将该项涂黑。
21. It can’t be denied that the Diaoyu Islands are _______ part of China and what some Japanese have done recently is actually a defence against _______ Chinese people.
A. a; / B. a; the C. the; / D. /; the
22. -- Have you been to the Great Wall?
-- Perhaps not in my memory. _______, it might have been during my early childhood.
A. If any B. If ever C. If once D. If not
23. — What did your parents think about your decision?
— They always let me do _______I think I should.
A. when B. that C. how D. what
