(a) Heavier

　　(b) Equally distributed

　　(c) Orderly

　　(d) Not uniform

　　17.  Why does the author mention "impact craters" in line 16?

　　(a) to show the result of the Moon not having an atmosphere

　　(b) to show the result of the Moon not having active tectonic or volcanic activity

　　(c) to explain why the Moon has no plant life because of meteorites

　　(d) to explain the corrosive effects of atmospheric weathering

　　18.   The word "erase" in line 19 is closest in meaning to

　　(a) change

　　(b) impact

　　(c) obliterate

　　(d) erupt

　　19.  A person on the Moon would weigh less than on the Earth because

　　(a) of the composition of lunar soil

　　(b) the surface gravity of the Moon is less

　　(c) the Moon has no atmosphere

　　(d) the Moon has no active tectonic or volcanic activity

　　20.  All of the following are true about the Moon EXCEPT

　　(a) it has a wide range of temperatures

　　(b) it is heavier on one side than the other

　　(c) it is unable to protect itself from meteorite attacks

　　(d) it has less effect upon the tides than the Sun

　　21.  Which of the following can be inferred from the passage?

　　(a) the Moon is not able to support human life

　　(b) if the Moon had no gravitational influence, the Earth would not have tides

　　(c) people living in Hawaii and Arizona would feel at home on the Moon

　　(d) Mars could have been formed in a similar way to the Moon