31. (A) Two different types of bones in the human body.

　　(B) How bones help the body move.

　　(C) How bones continuously repair themselves.

　　(D) The chemical composition of human bones.

　　32. (A) They defend the bone against viruses.

　　(B) They prevent oxygen from entering the bone.

　　(C) They break down bone tissue.

　　(D) They connect the bone to muscle tissue.

　　33. (A) They have difficulty identifying these cells.

　　(B) They aren't sure how these cells work.

　　(C) They've learned how to reproduce these cells.

　　(D) They've found similar cells in other species.

　　34. (A) To learn how to prevent a bone disease.

　　(B) To understand differences between bone tissue and other tissue.

　　(C) To find out how specialized bone cells have evolved.

　　(D) To create artificial bone tissue.

　　35. (A) A new fuel for buses.

　　(B) The causes of air pollution.

　　(C) A way to improve fuel efficiency in buses.

　　(D) Careers in environmental engineering.

　　36. (A) Her car is being repaired.

　　(B) She wants to help reduce pollution.

　　(C) Parking is difficult in the city.

　　(D) The cost of fuel has increased.

　　37. (A) A fuel that bums cleanly.

　　(B) An oil additive that helps cool engines.

　　(C) A material from which filters are made.

　　(D) An insulating material sprayed on engine parts.

　　38. (A) The high temperatures required for its use.

　　(B) The high cost of materials used in its production.

　　(C) The lack of trained environmental engineers.

　　(D) The opposition of automobile manufacturers.

　　39. (A) To present an award to a musician.

　　(B) To thank the organizers of "Time Out for the Arts."

　　(C) To invite musicians to join the concert tour.

　　(D) To introduce the guest speaker for the evening.

　　40. (A) The pianist is an old friend of hers.

　　(B) Many people have come to the presentation.

　　(C) The auditorium has an excellent sound system.

　　(D) She enjoys going to concerts.