问题 选择题

如图所示,是点电荷电场中的一条电场线,则(  )

A.a点场强一定大于b点场强

B.形成这个电场的电荷一定带正电

C.在b点由静止释放一个电子,将一定向a点运动

D.正电荷由b点从静止开始运动,将一定向a点运动

答案

A、未标明是正电荷还是负电荷的电场线,故a点场强、b点场强大小不一定,故A错误.

   B、根据电场线始于正电荷终止于无限远或负电荷,或电场线始于无限远终止于负电荷,此题无法确定电性,故B错误.

  C、根据电场强度的方向规定,正电荷受电场力的方向为电场强度的方向,负电荷受力则逆着电场线的方向,即由b点指向a点,故C正确.

  D、同C可知,D错误.

故选C

阅读理解

阅读理解

     Without proper planning, tourism can cause problems. For example, too many tourists can crowd

public places that are also enjoyed by the inhabitants of a country. If tourists create too much traffic,

the inhabitants become annoyed and unhappy. They begin to dislike tourists and to treat them impolitely.

They forget how much tourism can help the country's economy. It is important to think about the people

of a destination country and how tourism affects them. Tourism should help a country, keep the customs

and beauty that attract tourists. Tourism should also advance the wealth and happiness of local inhabitants.

     Too much tourism can be a problem. If tourism grows too quickly, people must leave other jobs to

work in the tourism industry. This means that other parts of the country's economy can suffer.

     On the other hand, if there is not enough tourism, people can lose jobs. Businesses can also lose

money. It costs a great deal of money to build large hotels, airports, air terminals, first- class roads, and

other support facilities(配套设施)needed by tourist attractions. For example, a major international class

tourism hotel can cost as much as 50 thousand dollars per room to build. If this room is not used most of

the time, the owners of the hotel lose money.

     Building a hotel is just a beginning. There must be many support facilities as well, including roads to

get to the hotel, electricity, sewers to handle waste, and water. All of these support facilities cost money.

If they are not used because there are not enough tourists, jobs and money are lost.

1. Which of the following do you think has been discussed in the part before this selection?

A. It is extremely important to develop tourism.

B. Building roads and hotels is essential.

C. Support facilities are highly necessary.   

D. Planning is of great importance to tourism.

2. Too much tourism can cause all these problems EXCEPT ____________ .

A. a bad effect on other industries      

B. a change of tourists' customs

C. over-crowdedness of places of interest

D. pressure on traffic

3. It can be inferred from the text that _____________ .

A. the author doesn't like tourism developing so fast

B. local people will benefit from tourist attraction

C. other parts of a country's economy won't benefit from tourism much

D. we can't build too many support facilities

4. The author thinks it is good for local people to know that tourism will ____________ .

A. waste a lot of money                  

B. weaken their economy

C. help establish their customs            

D. help improve their life

单项选择题