43. Why do swine flu viruses change constantly?
(A) The weather in the United States is changeable.
(B) The symptoms of swine flu change in different seasons.
(C)Influenza viruses from different species exchange their genes.
(D) The main virus subtypes change their genetic structures automatically.

39. For the performance, he practices ______ the lines over and over again. (A) say (B) to say (C)saying (D) said

40. ______ , we have to try our level best. (A) Be it work or play (B) Being work or play (C)To work or play (D) When work or play

41. What might be the author’s primary purpose of writing this passage? (A) To guarantee that swine flu viruses do not infect humans. (B) To testify that swine flu is the main cause of pigs’ death in the United States. (C)To show the urgent need of inventing specific vaccines to save pigs from being infected. (D) To introduce some basic information about swine flu viruses and how the flu can be prevented.

42. When do most outbreaks of swine flu happen? (A) They tend to happen on warm days. (B) They solely happen in late winter. (C)They mainly happen in the late fall and winter. (D) It depends on when the outbreaks will affect humans.

44. Which of the following symptoms is probably NOT a sign of swine flu in pigs? (A) Feeling itchy. (B) Having red eyes. (C)Having high temperature. (D) Sending out liquids from eyes.

45. According to the passage, what is the most possible way to prevent pigs from being infected by particular swine flu? (A) Keep pigs outside in winter days. (B) Inject specific vaccines into pigs. (C)Feed pigs on soft drink and bread. (D) Invite vets to examine pigs every fall.

46. (A) amaze (B) to amaze (C) amazing (D) amazed

47. (A) affected (B) separate (C)foreign (D) effective

48. (A) lives (B) is living (C)lived (D) live

49. (A) Form (B) To form (C)Forming (D) Formed