3. On the other hand, in the course of the evolution of birds from reptiles, there was a succession of changes in the bone, muscle, and skin structures of the animals. This wholesale restructuring of some reptiles over a period of thousands of years equipped the new animals to escape their predators and to find food more easily. But the evolutionary process did not stop there. Once adapted to flight, some birds continued to change and the process seemed to reverse itself. As penguins adapted to marine life, their wings changed to flippers and their feathers to a waterproof covering, thus suiting the birds for a semi-aquatic existence.

41. The Age of Mammals began when       .
A. animals evolved from reptiles
B. animals nursed the young
C. animals were more tolerant to external temperature
D. the dominant dinosaurs died out

42. It can be concluded from this passage that the ancestors of whales       .
A. were fish       B. chased reptiles
C. lived on the land      D. had too many offspring

43. In paragraph 2, the word ‘aquatic’ is closest in meaning to       .
A. of earth       B. of land
C. of river       D. of water

44. In paragraph 3, the word ‘succession’ is closest in meaning to       .
A. completion       B. series
C. addition       D. achievements

45. Certain reptiles gradually became able to escape quickly by       .
A. acquiring new structural features
B. becoming smaller and stronger
C. finding food more easily
D. changing their eating habits

46. Penguins are        .
A. sea birds        B. birds on land
C. reptiles        D. mammals

47. What is one of the changes in the course of the evolution of birds from reptiles?
A. Blood temperature.      B. Body surface.
C. Skin color.        D. Bone structure.

48. Whales and Penguins have something in common in their       .
A. flying         B. swimming
C. adaptation to nature      D. skin structure

49. According to the passage, which statement is true?
A. Birds and mammals developed from reptiles.
B. Reptiles use birds’ eggs as a source of food.
C. Birds adapted to living with reptiles.
D. Mammals are more tolerant to different types of food.

50. Which of the following would be the best title for this passage?
A. The Evolution of Mammals.
B. The Evolution of Life on Earth.
C. The Disappearance of Reptiles.
D. The Adaptation of Whales and Penguins.

Passage 4

1. The temperature of the Sun is over 5,000 degrees Fahrenheit at the surface, but it rises to perhaps more than 16 million degrees at the center. The Sun is so much hotter than the Earth that matter can exist only as a gas, except at the core. In the core of the Sun, the pressures are so great against the gases that, despite the high temperature, there may be a small solid core. However, no one really knows, since the center of the Sun can never be directly observed.