第二部分：单项填空（共15小题；每小题1分，满分15分）
21. The new law has come into effect, and _____ number of wild animals here is on _____ increase.
A. a; the B. a; / C. the; the D. the; /
22. She opened the door quietly so as not to _______ the sleeping baby.
A. interrupt B. disturb C. bother D. trouble
23. In China, the new couple are often dressed in red as it is a _____of good fortune.
A. sign B. symbol C. signal D. slogan
24. London is the only city in the world _______ taking a taxi is an interesting experience for tourists.
A. where B. that C. which D. whose
25. A person, when _______, can often do what is normally beyond his ability.
A. challenged B. challenges C. challenging D. to challenge
