题目内容：

    Mercury(水星) is the closest planet to the sun. It is a planet slightly larger than the Earth’s moon. It is covered in craters. Some craters have ice in them, even though the planet is hot. Sunlight never touches some parts because of the planet’s special position. Without air, there are great temperature differences between the coldest and hottest parts. Mercury days are so long that there are big differences between temperatures on the daylight side and the night side.

Mercury was created billions of years ago, when big rocks ran into each other. After these accidents, the planet was frequently visited by meteorites (流星) for several hundred million years. There were also many volcanic eruptions. As the planet cooled, the thin, rocky outside shell reduced in diameter(直径) by about 3 kilometers.

The Caloris Basin is one of the largest craters on Mercury. This big crater is 1, 300 kilometers wide and was formed when a large rock, about 100 kilometers across, knocked into the surface. Beethoven, another large crater, is 643 kilometers across.

The cliffs on Mercury are up to 2 kilometers high and hundreds of kilometers long. The cliffs were formed when the thin surface fell apart, as volcanic activity slowed down and Mercury became cooler.

One Mercury day lasts about 59 Earth days. Mercury takes about 88 Earth days to have a complete year, instead of the 365 days that we have on the Earth. Mercury speeds around the sun so that there are three Mercury days every two Mercury years! Mercury has a strange relationship with the Earth. Every 117 days, when Mercury is closest to the Earth, it always has the same side facing us.

Mariner 10 is the only spacecraft to visit Mercury. It made three visits to Mercury in, the 1970s, taking photos of many cliffs and craters. Although the first three visits answered many questions, they have raised others.

1.What is the surface of Mercury like?

A.It’s generally flat. B.It’s hot everywhere.

C.It’s bright everywhere. D.It’s cold in some parts.

2.Why did Mercury’s diameter get smaller?

A.A drop in temperature changed its size.

B.A great many meteorites ran into it.

C.It got out of shape as time passed.

D.Lots of surface rocks fell off.

3.What do we know about Mercury?

A.One Mercury day lasts about 88 Earth days.

B.It turns around the sun faster than the Earth.

C.Six Mercury days are two Mercury years.

D.It has more cliffs than large craters.

4.What happened after Mariner 10’s three visits to Mercury?

A.Another spacecraft visited Mercury.

B.New cliffs and craters were formed.

C.New signs of volcanic activity appeared.

D.Lots of new puzzles needed to be solved.