[单项选择]The gravitational pull of the earth and moon is important to us as we attempt to conquer more and more of outer space. Here’s why.
As a rocket leaves the earth, the pull of the earth on it becomes less and less as the rocket roars out into space. If you imagine a line between the earth and the moon, there’s a point somewhere along that line, nearer to the moon than to the earth, at which the gravitational pull of both the earth and the moon on an object is just about equal. An object placed on the moon side of that point would be drawn to the moon. An object placed on the earth side of that point would be drawn to the earth. Therefore, a rocket need be sent only to this "point of no return" in order to get it to the moon. The moon’s gravity will pull it the rest of the way.
The return trip of the rocket to the earth is, in some ways, less of a problem. The earth’s gravitational field reaches far closer to the moon than does the moon’s to earth. Thus, it will be necessary to f
A. the rocket
B. the pull of the earth
C. the pull of the moon
D. the gravitational pull of the earth and moon

[单项选择]The gravitational pull of the earth and moon is important to us as we attempt to conquer more and more of outer space. Here’s why.
As a rocket leaves the earth, the pull of the earth on it becomes less and less as the rocket roars out into space. If you imagine a line between the earth and the moon, there’s a point somewhere along that line, nearer to the moon than to the earth, at which the gravitational pull of both the earth and the moon on an object is just about equal. An object placed on the moon side of that point would be drawn to the moon. An object placed on the earth side of that point would be drawn to the earth. Therefore, a rocket need be sent only to this "point of no return" in order to get it to the moon. The moon’s gravity will pull it the rest of the way.
The return trip of the rocket to the earth is, in some ways, less of a problem. The earth’s gravitational field reaches far closer to the moon than does the moon’s to earth. Thus, it will be necessary to f
A. it reaches the "black hole"
B. it is caught in the gravitational field of another planet
C. it runs out of fuel
D. it explodes

[单项选择]Dark Forces Dominate Universe The earth．moon．sun and all visible stars in the sky make up less than one percent of the universe．Almost all the rest is dark matter and dark energy，unknown forces that ______(51)astronomers． Observations in recent years have changed the basic______ (52)of how the universe evolved and have indicated how little is known about the major forces and substances that______ (53) our world Astronomers now know that luminous(发光的)matter—stars，planets and hot gas----Accounts ______ (54) only about 0,4 percent of the universe．Non-luminous components，such as black holes and intergalactic(星系间的)gas，______ (55)up 3.6 percent The rest is either dark matter , about 23 percent，or dark energy，about 73 percent． Dark matter．Sometimes ______ (56)“cold dark matter，”has been known for some time．Only recently have researchers come to understand the key role it ______ (57)formation of stars，planets and even people． We ______ (58) our very existence to dark matter,” said phy
A. worry
B. move
C. puzzle
D. reject