Every object has weight. But the center of its weight is not always in the middle of the object. If the top of an object is heavier than its bottom, it will fall over easily. We say that its center of gravity is high. But if the bottom is heavier, it won’t fall easily. Then we say that its center of gravity is low.

Look at the first picture. This empty box must fall over, because its center of gravity (C) is not above the line of its bottom (AB).

Now look at the second picture. There is some heavy iron in the bottom of this box. It will not fall, because its center of gravity is above its bottom.

1.If the bottom of an object is ______ its top, it will fall over easily.

A. lighter than　　 B. heavier than　　 C. no heavier than　　  D. as heavy as

2.Please point out which box will not fall.

3.The main idea of the passage is _________.

A. why things fall over　　　　         B. a low center of gravity

C. a high center of gravity　　             D. that everything has weight

阅读理解

It's sometimes reported that strange objects have been seen high up in the sky. These unidentified(未确认的) flying objects - UFOs have made a lot of people interested. Some of the reports about them are difficult to believe.Some have been explained in scientific ways, others have never been explained.

　　It is not easy to decide whether a report is true or not. One report of UFOs came from a British plane on its way from New York to London in 1954. The British plane was flying over an island at 19,000 feet when the captain noticed that something was on their left and a little lower than their plane. It's about five miles away.

　　"It was not one object but several," the captain said. "We saw one large and six smaller objects. I sent a radio to report about them and I received the answer that the other planes were coming out to meet us. Before the planes arrived, the smaller objects entered the big objects. The big object then became smaller and moved away fast."

1.Some_____ have been explained in scientific ways.

2. In 1954, a British plane met a UFO when it was flying from_____ to_____.

3. The captain_____ and saw something on the left of their plane.

4. How many objects did the captain see?

5. The big object moved away because_____.

We call the baby panda Xi Wang. Xi Wang in this sentence is________.

　    A. Direct Object           B. Indirect Object  C. Object Complement  D. Attributive

Every object has weight. But the center of its weight is not always in the middle of the object. If the top of an object is heavier than its bottom, it will fall over easily. We say that its center of gravity is high. But if the bottom is heavier, it won’t fall easily. Then we say that its center of gravity is low.
Look at the first picture. This empty box must fall over, because its center of gravity (C) is not above the line of its bottom (AB).
Now look at the second picture. There is some heavy iron in the bottom of this box. It will not fall, because its center of gravity is above its bottom.

【小题1】If the bottom of an object is ______ its top, it will fall over easily.

We call the baby panda Xi Wang. Xi Wang in this sentence is________.

　    A. Direct Object           B. Indirect Object  C. Object Complement  D. Attributive