( ) 21. The country has already sent up three unmanned spacecrafts£¬ the most recent ¡¡¡¡¡¡¡¡ at the end of last March.
A. has been launched B. having been launched
C. being launched D. to be launched
( ) 22. Many children may be fond of animals£¬ but ¡¡¡¡¡¡¡¡ ever think of making the study of animals their career.
A. a few B. few C. some D. any
( ) 23. My wallet isn’t in my bag. Where ¡¡¡¡¡¡¡¡ I have put it£¿
A. can B. must C. should D. shall
( ) 24. The book was written in 1946£¬ ¡¡¡¡¡¡¡¡ the education system has witnessed great changes.
A. when B. during which C. since then D. since when