The sun today is a yellow dwarf sta

The sun today is a yellow dwarf star. It is fueled by thermonuclear reactions near its center that convert hydrogen to helium. The sun has existed in its present state for about four billion six hundred million years and is thousands of times larger than the earth.
By studying other stars, astronomers can predict what the rest of the sun’s life will be like. About five billion years from now, the core of the sun will shrink and become hotter. The surface temperature will fall. The higher temperature of the center will increase the rate of thermonuclear reactions. The outer regions of the sun will expand approximately 35 million miles, about the distance to Mercury, which is the closest planet to the sun. the sun will then be a red giant star. Temperature on the earth will become too high for life to exist.
Once the sun has used up its thermonuclear energy as a red giant, it will begin to shrink. After it shrinks to the size of the Earth, it will become a white dwarf star. The sun may throw off huge amounts of gases in violent eruptions called nova explosions as it change from a red giant to a white dwarf.
After billions of years as a white dwarf, the sun will have used up all its fuel and will have lost its heat. Such a star is called a black dwarf. After the sun has become a black dwarf, the Earth will be dark and cold. If any atmosphere remains there, it will have frozen over the Earth’s surface.
61. It can be inferred from the passage that the sun …………………
A. has been in existence for 10 billion years
B. is approximately halfway through its life as a yellow dwarf
C. will continue to be a yellow dwarf for another 10 billion years
D. is rapidly changing in size and brightness
62. What will probably be the first stage of change for the sun to become a red giant?
A. its core will cool off and use less fuel
B. its central part will grow smaller and hotter.
C. it will throw off huge amounts of gases
D. its surface will become hotter and shrink
63. When the Sun becomes a red giant, what will the atmosphere be like on the Earth?
A. it will become too hot for life to exist.
B. it will be enveloped in the expanding surface of the sun
C. it will freeze and become solid.
D. it will be almost destroyed by nova explosions.
64. When the sun has used up its energy as a red giant, it will………..
A. stop to expand
B. cease to exist
C. become smaller
D. get frozen
65. Large amounts of gases may be released from the Sun at the end of its life as a………………
A. white dwarf
B. red giant
C. yellow dwarf
D. black dwarf
66. As a white dwarf, the Sun will be …………..
A. a cool and habitable planet.
B. the same size as the planet Mercury
C. thousands of times smaller than it is today.
D. around 35 million miles in diameter.
67. the sun will become a black dwarf when …………..
A. the outer regions of the Sun expand
B. it has used up its fuel as a white dwarf
C. the sun moves nearer to the Earth
D. the core of the Sun becomes hotter.
68. the word “there” in the last sentence of paragraph 4 refers to ……………………….
A. our own planet
B. the core of a blank dwarf
C. the outer surface of the Sun
D. the planet Mercury.
69. this passage is intended to ……………………
A. describe the changes that the Sun will go through
B. discuss conditions on the Earth in the far future
C. alert people to the dangers posed by the Sun
D. present a theory about red giant stars
70. the passage has probably been taken from………………….
A. a scientific chronicle
B. a news report
C. a work of science fiction
D. a scientific journal.