单选题 Directions: After reading the following passage, you will find 5 unfinished statements or questions. For each statement there are four choices marked A, B, C and D, you should make the best choice and mark the corresponding letter on the Answer Sheet with a single line through the center.
Are there snowballs in space? Many astronomers think that comets — those heavenly bodies with long bright tails — may be "dirty snowballs" trailing specks of ice and dust. For some time astronomers have figured that the small head of a comet is made up of frozen gases, ice, and dust particles. Now astronomers say that comets may not be the only "dirty snowballs" in space.
Two research teams of astronomers studied the light reflected or bounced back from the moons of the planet Saturn. The two teams used different equipment. But they got similar results. Both teams found evidence that at least three of Saturn's ten moons may be "dirty snowballs." The moons — named Rhea, Dione, and Tethys — seem to be made up mostly of water, ice, and dust particles.
Could other even larger moons also be "dirty snowballs"? Maybe. Meanwhile, if the astronomers are right, then Rhea, Dione, and Tethys just might be the largest "ice cubes" in our solar system.
单选题 Comets are ______.
  • A. small planets
  • B. large moons
  • C. heavenly bodies with tails
  • D. objects made up of only dust particles
【正确答案】 C
【答案解析】[解析] 答案的依据在第一段的第二句，破折号之间的部分：those heavenly bodies with long bright tails是对comets的解释。也就是说，彗星是带尾巴的天体。
单选题 The head of a comet contains ______.
  • A. frozen gases and ice
  • B. frozen gases, ice and dust particles
  • C. dust particles
  • D. neither frozen gases, ice nor dust particles
【正确答案】 B
【答案解析】[解析] 根据第一段的第三句可知。彗星的头部是由冻结了的气体、冰和尘粒组成。故确定B为正确答案。
单选题 Two teams of astronomers studied the ______.
  • A. paths of comets
  • B. path of Saturn
  • C. heads of comets
  • D. moons of Saturn
【正确答案】 D
【答案解析】[解析] 根据第二段的第一句：“两个由天文学家组成的研究小组对从土星的卫星反射回的光进行了研究。”确定本题正确答案为D。
单选题 What was the new discovery made by the two teams of astronomers?
  • A. Most comets are made up of water, ice and dust.
  • B. Three of Saturn's moons may be made up of water, ice and dust
  • C. Many large moons may be made up of water, ice and dust.
  • D. Not any "ice cubes" exist in our solar system.
【正确答案】 B
【答案解析】[解析] 本题答案的依据是第二段的最后两句。这两句话的意思是：“两个由天文学家组成的研究小组发现，有证据表明土星的十个卫星中至少有三个可能主要是由水、冰和尘粒组成的‘脏雪球’。”所以，两组天文学家作出的新发现是三个土星的卫星可能是由水、冰和尘粒组成。
单选题 The largest "dirty snowballs" in space are ______.
  • A. the moons of Saturn
  • B. comets
  • C. Rhea, Dione, and Tethys
  • D. not mentioned in the article
【正确答案】 C
【答案解析】[解析] 确定本题答案的依据是最后一段中的：...Rhea, Dione, and Tethys just might be the largest "ice cubes" in our solar system. 也就是说，叫做Rhea，Dione和Tethys的土星的三个卫星完全有可能是太空中最大的“脏雪球”。