21 To me, cycling at ___ altitude of more than 4,000 meters was _____ unforgettable experience.
A. the; an B. an; an C. /; a D. an; /
22. Some people do not have enough to eat while some others throw away food just______ its poor taste.
A. because of B. according to C. instead of D. in spite of
23. To improve your spoken English, you’d better listen to the tape __________.
A. generally B. fluently C. frequently D. gradually
