Touring the nine planets

We live within a system of nine planets, all of which circle our Sun. This system, as you probably learned in school, is called the solar system. Those planets are, in order of their proximity to the Sun: Mercury, Venus, Earth, Jupiter, Saturn, Uranus, Neptune and Pluto.

Even though man has set foot on only one planet, the human race has sent a number of unmanned space probes to visit every planet – except for Pluto. We’ve soft-landed on Venus and Mars, and completely mapped them and the planet Mercury. Mapping Venus was a challenge because it is forever and completely covered by sick clouds that we cannot see through with conventional methods. We’ve flown and obtained some very beautiful photographs of Jupiter, Saturn, Uranus, and Neptune. We even flew right through the rings of Saturn!

The nine planets were all formed between four and five billions years ago, just about the same time as the Sun. Matter going around the central point of the solar system finally condensed to form the sun. But gases and some heavier elements, in the form of dust, also began swirling about centralized areas of their won and started getting together. They produced their own gravity, which attracted even more matter. In this way, the planets of our solar system were born.来源：考试大

The inner planets – Mercury Venus, Earth, and Mars – have solid sores. With the exception of Pluto, the outer planets – Jupiter Saturn, Uranus, and Neptune –are known as gas giants. We can never land on them. They have no solid core and are made only of various gases. But that doesn’t mean that we could fly through them in a spacecraft, either. Even though they are made only of gas that gas has weight and mass also. These planets are so massive that they exerting quite a force at their center, or core.

1. Among the solar system, Mercury is the closest to the sun, while Pluto is the farthest from the sun.
A. right   B. wrong  C not mentioned来源：考试大

2. So far man has made great progress in space exploration.
A. right   B. wrong  C not mentioned来源：考试大

3. People have tried to soft-landed on the planet Mercury but failed to make it.
A. right   B. wrong  C not mentioned来源：考试大

4. The Sun was formed earlier than any of the nine planets.
A. right   B. wrong  C not mentioned

5. Mapping Venus is difficult because the planet is so hot that spacemen could not land on it.
A. right   B. wrong  C not mentioned来源：考试大

6. The only reason why it is impossible to land on the outer space is that the outer planets are not solid and made of gases.
A. right   B. wrong  C not mentioned来源：考试大

7. Man will be able to fly through the outer planets in a spacecraft sooner or later.
A. right   B. wrong  C not mentioned