the chair is very comfortable to sit on该句中的不定式与主语有动宾关系，因此必须是及物动词，不及物动词则该加上适当的介词。

动词的分类：行为/实义动词、及物与不及物动词、瞬时与持续动词、状态与动作动词、 助动词、情态动词与连系动词

1. There is someone knocking at/on the door. Who ________ it be?

  A) may            B) will            C) can          D) must

  It is natural that children are curious about the world around them. For example, they want to know how their hearts beat. They want to know why the ocean water tastes salty.

　As children grow up, they become curious about different kinds of things. When they are babies, they are interested in the parts of their bodies and in the smiles of their mothers. They become interested in the physical world around them: the plants, the animals, the sky. Later, they become interested in the things that people have made: wheels, bicycles, cars. And when they are adults, their curiosity continues. Sometimes this curiosity leads to a career in science.

　Scientists spend their lives trying to find out about the world. Those who work with the earth sciences study the earth, the oceans, and the sky. Other scientists who study living things work with the biological sciences. A third group of scientists study the physical sciences, e. g. physics, chemistry .

　These scientists have already discovered a lot about our world. For example, they tell us why your heart beats fast when you run. They say that when you are quiet, your heart normally beats 65 or 75 times a minute. Your heart is a pump that pumps blood to all parts of the body. The blood carries oxygen and nutrition. When you run, your muscles work very hard and use the nutrition that the blood carries to them. The muscles need oxygen, too. So your brain sends a signal to the heart. The signal means that the muscles need more nutrition and oxygen. Then the heart beats fast and sends blood quickly to the muscles. It may beat 90 to 140 times a minute.

　Of course, scientists cannot answer all of our questions. If we ask, “Why does the ocean water taste salty” scientists will say that the salt comes from rocks. When a rock gets very hot or very cold, it cracks. Rain falls into cracks. The rain then carries the salt into the earth and into the rivers. The rivers carry the salt into the ocean. But then we ask , “What happens to the salt in the ocean? The ocean does not get saltier every year.” Scientists are not sure about the answer to this question.

　We know a lot about our world, but there are still many answers that we do not have, and we are curious.

According to the passage, which of the following statements is true?

　 A. People are curious in the same way.

　 B. People in different countries are interested in different things.

　 C. People of different ages are interested in different things.　 

   D. Men and women are curious about different things.

Scientists who work with the biological sciences study____.

   A. the earth , the oceans and the sky    B. plants and animals

   C. man-made things                 D. ocean water

A rock cracks _____.

   A. in wet regions                   B. in dry regions

   C. when salty water falls in           D. at very high or very low temperatures

People are always curious because _____ .

A. they know little about the world     B. they know nothing about the world

C. they can not explain many things     D. they want to be scientists

　Most people feel lonely sometimes, but it usually only lasts between a few minutes and a few hours. This kind of loneliness is not serious. In fact, it is quite normal. For some people, though, loneliness can last for yeas. Now researchers say there are three different types of loneliness.
　　The first kind of loneliness is temporary（暂时的）. This is the most common type. It usually disappears quickly and does not require any special attention. The second kind, situational loneliness, is a natural result of a particular situation-for example, family problem, the death of a loved one, or moving to a new place. Although this kind of loneliness can cause physical problems, such as headaches and sleeplessness, it usually does not last for more than a year.
　　The third kind of loneliness is the most severe. Unlike the second type, chronic（长期的）usually lasts more than two years and has no specific cause. People who experience habitual loneliness have problems socializing and becoming close to others. Unfortunately, many chronically lonely people think there is little or nothing they can do to improve their condition.
Psychologists agree that one important factor in loneliness is a person's social contacts, e.g. friends, family members, co-workers, etc. we depend on various people for different reasons. For instance, our families give us emotional support, our parents and teachers give us guidance, and our friends share similar interests and activities. However, psychologists have found that, though lonely people may have many social contacts, they sometimes feel they should have more. They question their popularity.
　　Psychologists are trying to find ways to help habitually lonely people for two reasons: they are unhappy and unable to socialize and there is a connection between chronic loneliness and serious illness such as heart disease. While temporary and situational loneliness can be normal, healthy part of life, chronic loneliness can be a sad, and sometimes dangerous condition.
【小题1】How would you treat temporary loneliness according to the passage?