A、 
B、 
C、 -cotx+C
D、 cotx+C
答案：C
解析：解析:
A、
B、
C、 -cotx+C
D、 cotx+C
答案：C
解析：解析:
A. 重要保障
B. 依靠力量
C. 国际基础
D. 必要条件
A. will see
B. be seen
C. have seen
D. have been seeing
A. to
B. at
C. for
D. of
A. went on
B. goes on
C. is going on
D. will go on
A. any city
B. any other city
C. any else city
D. any rest city
解析：解析:populous 人口众多的解析:单数一定要跟单数比。
A. require
B. ask
C. encourage
D. permit
解析：解析:stay out 不回家解析:require 要求Ask 要求解析:encourage 鼓励解析:permit 允许
A. have shut up
B. had shut up
C. have been shut up
D. had been shut up
