Section 2: Reading Comprehension (55 Points, 75 minutes)
In this section you will find after each of the passages a number of questions or unfinished statements about the passage, each with four (A. B. C and D) suggested answers or ways of finishing. You must choose the one which you think fits best. Then mark the corresponding letter with a single bar across the square brackets on your Machine-scoring ANSWER SHEET.
Questions 51-56 are based on the following passage.
As viewed from space, the Earth's distinguishing characteristics are its blue waters and white clouds. Enveloped by an ocean of air consisting of 78% nitrogen and 21% oxygen, the planet is the only one in our solar system known to harbor life. Circling the Sun at an average distance of 149 million km (93 million miles), the Earth is the third planet from the Sun and the fifth largest planet in the solar system. Its rapid spin and molten nickel-iron core give rise to an extensive magnetic field which, coupled with the atmosphere, shields us from nearly all of the harmful radiation coming from the Sun and other stars. Most meteors burn up in the Earth's atmosphere before they can strike the surface. The planet's active geological processes have left no evidence of the ancient pelting it almost certainly received soon after it was formed. The Earth has a single natural satellite -- the Moon.
（责任编辑:秩名）
