21. China is developing at such an astonishing _____ that it takes on a new look every day.
A. altitude B. achievement C. rate D. direction
22. Mr. Black had a stomachache for a long time, so he decided to _____ his doctor and find out the problem.
A. admire B. encourage C. greet D. consult
23. After years of careful observation in the wild, Jane Goodall was finally able to _____ the social system of chimps.
A. carry out B. pick out C. look out D. work out
