At Home in Space?

　　But in space, without special protection, we would be exposed to much stronger radiation from ultraviolet light and cosmic rays. Also, in the zero gravity of outer space, our bones will lose calcium and become weaker. This will be more of a problem the longer people stay out in space. Doctors are looking for a way to keep our bones from losing calcium in outer space. And a small spaceship just might “drive you batty” after a while. But even on a short trip in outer space, you might not feel as well as you’d like to. Space travel could make you seasick!

　　Yet, these risks won’t keep people from going into space. Eventually, an Earth-like environment will be built in space. And they will be populated by people with many different interests: medicine, construction, farming, teaching, mining, and so on。

　　The next hundred years will be filled with other worldly adventures, exciting scientific discoveries, and danger, as humans leave Earth—perhaps forever。

　　Aging in Space

　　Suppose a space traveler is moving at a velocity of 186,200 miles per second. For every hour that passes for him, 30 hours pass on Earth. If he travels for a year in this fashion (having accelerated instantaneously) and then turns around and comes back at this speed (having turned around instantaneously)， he will find that while he has seemed to himself to have traveled two years, the men on Earth would claim he had been absent for 30 years。

　　Suppose the space traveler had left at the age of 30, leaving behind a twin brother also aged 30. When he returned he would be 32, but his stay-at-home twin brother would be 60. That is why the “clock paradox”， is sometimes called the “twin paradox”。

　　Of course it takes quite a long while to accelerate to a high speed, and a long while to make a turn and head back again, so conditions aren’t quite as clear�瞔ut as just described。

　　1.The giant, spherical spaceship mentioned in the passage is。

　　[A]the outer space[B]a man-made spaceship

　　[C]the planet Earth[D]the Star Wars mother-ship

　　2.Some persons have traveled into outer space after conqueringwithin the past 25 years。

　　[A]the universe[B]Earth’s gravity

　　[C]the earth [D]outer space

　　3.We have explored or sent robot spaceships to the following space except。

　　[A]the moon[B]Venus[C]Jupiter[D]Mars

　　4.Why is the conquest of space more than a great adventure?

　　[A]Because it is full of challenges for human beings。

　　[B]Because it may be necessary for human beings to survive。

　　[C]Because it is the greatest adventure in human history。

　　[D]Because it is more exciting than any other adventures。

　　5.The moon and the asteroids are alike with respect to their 。

　　[A]size and moving ways [B]comfortable living conditions

　　[C]rich and valuable metals[D]solar energy

　　6.Why can’t ultraviolet light scorch our skin on Earth as seriously as it does in space places?

　　[A]Because the Earth’s atmosphere can make ultraviolet light less harmful。

　　[B]Because ultraviolet can’t reach the Earth at all。

　　[C]Because the Earth is far away from those planets radiating ultraviolet light。

　　[D]Because other space places is near from those planets radiating ultraviolet light。

　　7.In spite of many risks, scientists will finally buildin space suitable for humans to live。

　　[A]an environment without ultraviolet light

　　[B]a lot of homes

　　[C]an Earth-like environment

　　[D]an environment with atmosphere

　　8.The reason some metal alloys can’t be made on Earth is that the heavier metals ___________together with the lighter ones。

　　9.In space, there is no atmosphere to filter out the sun’s energy. There is plenty of solar energy to be turned into_____________ , for creating comfortable living conditions。

　　10.According to the author,__________________ will be caused to a man in gravity-free space。