问题 选择题

划船时,使船和桨一起向前运动的力是(  )

A.河中的水对桨的力

B.划船的人对桨的力

C.船桨对水的力

D.船对水的推力

答案

划船时,船桨向后划水,给水一个向后的力,物体间力的作用是相互的,水会给船桨一个向前的推力,这样船就前进了,水对浆的推力是船前进的动力.

故选A.

单项选择题
阅读理解

阅读理解。

     Ever since they were first put on the market in the early 1990s, genetically modified (GM, 转基因) foods

have been increasingly developed and marketed in many countries in the word, mainly on the basis of their

promise to end the worldwide food crisis. But can GM technology solve world hunger problems? Even if it

would, is it the best solution?

     Despite what it promises, GM technology actually has not increased the production potential of any corp.

In fact, studies show that the most crown GM crop.

     GM soybeans, has suffered reduced productivity. For instance, a report than analyzed nearly two decades

of research on major GM food crops shows that GM engineering has failed to significantly increase US crop

production.

     Something else, however, has been on the rise, While GM seeds are expensive, GM companies tell farmers

that they will make good profits by saving money on pesticides (杀虫剂). On the contrary, US government

data show that GM crops in the US have produced an overall increase in pesticide use compared to traditional

crops. "The promise was that you could use less chemicals and boost production. But neither is true," said Bill

Christenson, President of the US National Farm Coalition.

     At the same time, the authors of the book World Hunger: Twelve Myths argue that there actually is more

than enough food in the world and that the hunger crisis is not caused by production, but by problems in food

distribution and politics. These indeed deserve our efforts and money. Meanwhile, the rise in food prices results

from the increased use of crops for fuel rather than food, according to a 2008 World Bank report.

     As a matter of fact, scientists see better ways to feed the world. Another World Bank report concluded that

GM crops have little to offer to the challenges of worldwide poverty and hunger, because better ways out are

available, among which "green" farming is supposed to be the first choice.

1. The author develops the second paragraph mainly _____.

A. by classification

B. by comparison

C. by example

D. by process

2. What does the underlined word "boost" in the third paragraph probably mean?

A. Control.

B. Evaluate.

C. Obtain.

D. Increase.

3. GM companies promise farmers that they will benefit from ______. 

A. practicing "green" farming

B. use of less chemicals

C. fair distribution of their crops

D. using more crops for fuel

4. Which of the following best describes the attitude of the author towards GM technology?

A. Optimistic

B. Defensive

C. Disapproving

D. Casual