21. Her teaching experience gave her a big a                 over the other applicants for the job.

22. They killed many sharks last year. How c                 they are!

23. When i                 is well developed in one country, the people there will be rich and live a better life.

24. This is a s                 experiment.

25. I saw the White House where the P                 of the USA lives.

26. I don't like lions because they're u                .

27. People throw l                 into the river and make it really dirty.

28. We should r                 the waste paper to protect the environment.

29. Living in the city has many a                 such as good schools, big shopping centers and so on.

30. The landlord is so c                 that almost everybody hates him.

31. It was her dream to enter the film i                 when Gong Li was very young.

32. Here are some things they have learned from s                (科学的) studies.

33. Obama is the P                 of the USA.

34. The lady is not beautiful at all. In fact, she is very u                .

35. If no one l                ,the park will be very clean.

36. It's important to r                (回收利用) paper to save the trees.

37. --- Do you know the a                 of this type of bicycle?

--- It's very light.

38. People generally think that he who kills a pet dog or a pet cat is c                .

39. The tourist i                 is developing rapidly in China.

40. So far, no s                 studies have shown that sharks fins are good for health.