21. according to
22. specialize in doing sth
23. serve as
24. at one time
25. tend to
26. interest in
27. due to
28. lead to
29. at least
30. contrary to
31. be equal to
32. contribute to doing sth
33. live in
34. be dedicated to doing
35. deal with
36. belong to
37. it is estimated that
38. be resistant to
39. result from
40. consist of