21. His whole income _________ no more than 1,000 yuan per month.
A. added up to B. added to C. is added up D. added.
22. ___________ sleep late in the morning, Bob turned off the alarm clock.
A. So as to B. So that C. In order to D. In order that
23. While _________ in the countryside, he made many friends with the native there.
A. worked B. working C. he works D. he is working
