第一节 单项填空（共15小题；每小题1分，满分15分） 21. to me, cycling at ____ altitude of about 4,500 meters is ____ unforgettable experience. a. the; an b. an; an c. 不填; 不填 d. an; 不填 22. — i am leaving for beijing to take part in a maths competition tomorrow. — ____. a. take care b. good luck c. have a nice trip d. congratulations
