问题 选择题

湖面上相距一定距离且完全相同的甲、乙两只小船,现用一根绳子将两船的船头相连.若两船上各坐一质量相等的人,当甲船上的人用力拉绳子时,将会出现(  )

A.乙船向甲船驶来

B.甲船向乙船靠去

C.甲、乙两船互相靠拢

D.甲、乙两船一定静止不动

答案

甲船上的人用力拉绳子时,乙船会在拉力的作用下,向甲船驶来;由于物体间力的作用是相互的,所以甲船上的人用力拉绳子时,同时也受到绳子对他的拉力,则甲船也会在绳子拉力的作用下,向乙船驶去;所以两船是互相靠拢.A和B错,C正确.

D、由于两船受到力的作用,所以船会由静止变为运动.

故选 C

名词解释
阅读理解

阅读理解。

    Millions of years ago there were many types of dinosaurs on earth. Most dinosaurs were plant-eaters.

The Apatosaurus, for example, had a long thin neck so that it could eat leaves from trees. Other dinosaurs

were meat-eaters. The Tyrannosaurus Rex killed smaller dinosaurs for food.

    Dinosaurs were real animals that once lived on the earth, but they died out about 65 million years ago.

The disappearance of the dinosaurs is in some way a great mystery (谜). Some scientists think that the

climate (气候) changed suddenly. Fossils (化石) of trees tell us that the temperature dropped a lot and that

the level of the sea dropped as well. This means that it got suddenly much colder. Perhaps the dinosaurs

were too slow to change with the climate.

    A new idea is that a meteor (流星) crashed into the earth. Scientists discovered a place in Mexico where

they think the meteor crashed. They think that there was a lot of dust from the meteor. The dust landed on

the plants.Also the dust blocked (阻挡) the sun's light for as long as five years. Many animals, including

dinosaurs, were plant-eaters, and perhaps the dust killed them. This means there was nothing left for meat-

eating dinosaurs to eat, and so they died out. But, as many animals from that time didn't die, we are not 100%

sure what really happened.

1. What is the subject discussed in the text? [ ]

A. Dinosaurs, the real animals living millions of years ago.

B. The two types of dinosaurs.

C. The probable reasons for dinosaurs disappearance.

D. A meteor crashed into the earth.

2. What are the two possible explanations to the dinosaurs disappearance? [ ]

A. Temperature dropping and sea level dropping.

B. Climate changing and meteor's crashing.

C. The dropping of temperature and sea level.

D. Climate changing and the dust blocking the sun.

3. What is the direct cause of the disappearance of meat-eating dinosaurs? [ ]

A. A meteor's crashing.

B. The dust blocking the sun.

C. The plant-eating dinosaurs death.

D. It is still unknown.