5.Directions: Read the following three passages. Each passage is followed by several questions or unfinished statements. For each of them there are four choices marked A, B, C and D. Choose the one that fits best according to the information given in the passage you have just read.

　　In 1801, Giuseppe Piazzi discovered a new object in the sky. He thought it was an undiscovered comet. After further observation, he realized that it behaved more like a small planet than a comet. Piazzi named it Ceres after the Sicillian goddess of grain. Ceres remains the largest known asteroids（小行星）in the sky. It means almost 600 miles（1,000 km） in diameter. By the end of the nineteenth century, several hundred other asteroids had been identified.

　　Tens of thousands of asteroids have since been discovered, with thousands more found each year. Asteroids are masses of rock and metal that orbit（绕轨道而行）the sun between Mars and Jupiter. They did not form into planets because the perturbations of Jupiter kept them moving too fast to join together. The total mass of all of the asteroids is less than the size of Earth’s moon.

　　Some of the asteroids move in orbits outside the zone between Mars and Jupiter. Asteroids that come relatively close to Earth are known as near-Earth asteroids（NEAs）. Scientists estimate that about 1,000 of these asteroids are 0.6 miles（1km） in diameter. An asteroid of this colliding（碰撞）with Earth would be disastrous.

　　Scientists have found two sites where giant asteroids struck Earth millions of years ago. One asteroid hit Antarctica about 250 million years ago. Another asteroid struck Mexico’s Yucantan Peninsula around 65 million years ago, leaving a hole 112 miles（180km） wide and 1,000 yards （915m） deep. One theory blames the extinction of the dinosaurs on this asteroids’s collision with Earth and the climate change that resulted from its impact.

　　Occasionally, small asteroids strike Earth. These cause little damage. Major collision, such as the one that may have killed the dinosaurs, occur rarely--perhaps only once every 100 million years.

　　Although the chance of an asteroid striking the planet anytime soon is small, scientists continue to study the orbits of asteroids in the sky. They pay particularly close attention to the asteroids whose paths are close to Earth, and have even landed a spacecraft on an NEA named Eros. Their work helps them learn about the formation of the solar system. It may even help them discover ways to avoid an asteroid disaster in the future.

（1）Which of the following statement is NOT true about asteroids?

A. Asteroids are composed of rock and metal.

B. Asteroids orbit the sun between Mars and Jupiter.

C. Large near-Earth asteroids are sure to strike Earth.

D. A large asteroid colliding with Earth would cause a disaster.

（2）The word “perturbations”（paragraph 2） is closest in meaning to “      ”.

A. Formation of rocks

B. Disturbance of motion

C. Estimation of scientists

D. Influences of size

（3）What scientists have found implies that

A. two sites of Earth hit giant asteroids millions of years ago

B. Antarctica was once struck by an asteroid millions of years ago

C. one asteroid left a huge hole in Mexico 250 million years ago

D. the extinction of dinosaurs resulted in asteroid’s collision with Earth

（4）Which of the following events happened third according to the passage?

A. Giuseppe Piazzi discovered a new object and name it Ceres.

B. Scientists had a spacecraft land on Eros to learn more about the solar system.

C. Asteroids orbiting the sun failed to form into planets.

D. Several hundred asteroids had been identified by the end of the nineteenth century.