74. It seems that the earth may face the danger of mass extinction_________.

a.　　　 every 65 million years

b.　　　 every 100 million years

c.　　　 once in a billion years　

d.　　　 once in 225 million years

73. The radiation produced by star collisions tends to__________.

a.　　　 burn out nearby planets

b.　　　 change the structure of the universe

c.　　　 destroy the atmosphere on nearby planets

d.　　　 kill everything in the universe

72. Collisions of stars take place in the universe_______.

a. occasionally　　　 b. daily　　 c. rarely　　　　 d. readily

71. The passage mainly deals with_______.

a.　　　 the collision of stars in space

b.　　　 the function of cosmic radiation

c.　　　 the protection of the earth’s atmosphere

d.　　　 the cause of the mass extinction of dinosaurs

70. a. wise　　 b. clever　 c. slow　 d. enough

Reading Comprehension

　　　　　　　　 A

　　　 A scientist in Israel has introduced a new theory that explains the mass extinction of the dinosaurs 65 million years ago. The scientist believes the criminal was deadly radiation caused by the collision of two stars.

　 Arnon Dar, a physicist at Technion University, says stars collide every day somewhere in the universe. Those collisions produce radiation-gamma and cosmic rays----with the potential to destroy the protective layers of Earth’s atmosphere and kill most animal and plant life.

　 Usually, the collisions are too distant to do any damage to life on earth. But once every 100 million years or so, stars collide relatively close to Earth. A nearby collision could have emitted enough gamma and cosmic rays to kill the dinosaurs, the scientist says. Star collisions could also have been the cause of the five other mass extinctions that have happened on Earth, he adds. The most severe die-off, which killed 95 percent of all life, happened about 225 million years ago.

　 To support his idea, the scientist is now looking through layers of ancient rock for mineral that show evidence of being bombarded by cosmic radiation 65 million years ago.

69. a. catching　　 b. caught　　 c. being caught　 d. having caught

68. a. relied on　　 b. relaxed　 c. freed　　 d. found

67. a. without　　 b. with　　 c. through　 c. for

66. a. ignorant of　　 b. blaming　 c. yielding to　　 d. turning a deaf ear to

65. a. talks about　 b. comes to　 c. turns to　 d. mentions