问题 选择题

在农田中试用某种农药防治害虫,使用年数越长,效果越差.对这一现象的下列解释正确的是(  )

A.农药使害虫发生了抵抗农药的变异

B.农药选择了害虫中能抵抗农药的变异

C.害虫会自然发生并巩固农药的变异

D.农药质量越来越差

答案

首先害虫存在两种变异品种:抗药能力强的害虫与抗药能力差的害虫.农药使害虫中抗药能力差的害虫死亡,而抗药能力强的害虫活了下来.这样控制抗药能力强的基因得到积累与加强,使用时间越长,效果越差,是因为农药选择了害虫中能抵抗农药的变异.

故选:B

阅读理解

Long ago, people lived on wild animals, fruits and other plants and they didn’t need to use money.

As time passed, families had more products(产品) than they needed, such as animals and crops. So they needed to trade(交易) with others. They began to use money to make it easier. However, it was not like the money we use today. They used shells, rice, salt or large stones.

During the 600s BC, people began using coins as money. Because they were easier to carry than goods(货物), countries began to make coins as their money.

The Chinese were the first to use paper money, probably in the 11th century. An Italian traveler, Marco Polo, saw the Chinese use paper money when he visited China in the 1200s. After his travel, he told the western people what he saw. But European countries didn’t start using paper money till the1600s.

Today we have many ways to pay for things, such as coins, paper money and cards. Some prefer to pay by card. That’s because paying with a card is easier and safer than carrying around a lot of “real” money.

小题1:People began to use money because they ______.

A. lived on plants           B. raised animals        C. needed to trade

小题2:People used ______ as money during the 600s BC.

A. shells                    B. coins                 C. cards

小题3:Which country used paper money first?

A. Japan.                    B. USA.                  C. China.

小题4:The passage tells us the ______ of money

A. history                   B. use                   C. collection

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