问题 选择题
电气化铁路的输电线常用图所示的方式悬挂在钢缆上.钢缆的A端固定在电杆上,B端连接在滑轮组上.滑轮组由a、b、c三个滑轮构成,配重P由多个混凝土圆盘悬挂在一起组成,配重的总重为G,若不计摩擦和滑轮的重量,则以下说法中正确的是(  )

A.a为动滑轮,B端钢缆受到滑轮组的拉力大小约为3G

B.a为动滑轮,B端钢缆受到滑轮组的拉力大小约为G

C.a、c为动滑轮,B端钢缆受到滑轮组的拉力大小约为3G

D.a、c为动滑轮,B端钢缆受到滑轮组的拉力大小约为G

答案

答案:A

阅读理解

阅读理解。

     In a world with limited land, water and other natural resources (资源), the harm from the traditional

business model is on the rise. Actually, the past decades has seen more and more forests disappearing

and globe becoming increasingly warm. People now realize that this unhealthy situation must be changed,

and that we must be able to develop in sustainable (可持续的) ways. That means growth with low

carbon or development of sustainable products. In other words, we should keep the earth healthy while

using its supply of natural resources.

     Today, sustainable development is a proper trend in many countries. According to a recent study, the

global market for low-carbon energy will become three times bigger over the next decades. China, for

example, has set its mind on leading that market, hoping to seize chances in the new round of the global

energy revolution. It is now trying hard to make full use of wind and solar energy, and is spending a huge

amount of money making electric cars and high-speed trains. In addition, we are also seeing great growth

in the global markets for sustainable products such as palm oil (棕榈油), which is produced without

cutting down valuable rainforest. In recent years the markets for sustainable products have grown by

more than 50%.

     Governments can fully develop the potential of these new markets. First, they can set high targets for

reducing carbon emissions (排放) and targets for saving and reusing energy. Besides, stronger

arrangement of public resources like forests can also help to speed up the development. Finally,

governments can avoid the huge expenses that are taking us in the wrong direction, and redirecting some

of those expenses can accelerate the change from traditional model to a sustainable one.

     The major challenge of this century is to find ways to meet the needs of growing population within the

limits if this single planet. That is no small task, but it offers abundant new chances for sustainable product

industries.

1. The traditional business model is harmful because of all the following EXCEPT that ______.

A. It makes the world warmer

B. it consumes natural resources

C. it brings severe damage to forests

D. it makes growth hard to continue

2. What can we infer from Paragraph 2?

A. China lacks wind and solar energy.

B. China is the leader of the low-carbon market.

C. High-speed trains are a low-carbon development.

D. Palm oil is made at the cost of valuable forests.

3. To full develop the low-carbon markets, government can ______.

A. cut public expenses

B. forbid carbon emission

C. develop public resources

D. encourage energy conservation

4. We can learn from the last paragraph that businesses have many chances to ______.

A. develop sustainable products

B. explore new natural resources

C. make full use of natural resources

D. deal with the major challenge

5. What is the main purpose of the passage?

A. To introduce a new business model.

B. To compare two business models.

C. To predict a change of the global market.

D. To advocate sustainable development.

单项选择题