题干

我们国家非常重视抗生素的规范使用,因为一种抗生素使用一段时间后,杀菌效果会下降,原因是细菌产生了抗药性.请用达尔文的自然选择学说解释细菌产生抗药性的原因(    )

A:细菌为了适应环境,产生了抗药性变异

B:细菌接触了抗生素后,慢慢产生了抗药性

C:抗生素对细菌的抗药性变异进行了定向选择

D:后来的抗生素的用量减少,细菌产生了抗药性变异

上一题 下一题 0.0难度 选择题 更新时间:2018-01-25 05:24:16

答案(点此获取答案解析)

C

同类题5

阅读理解

      The Internet, mobile phones and Ipads are part of our lives now. Technology is greatly affecting all ways of our lives, from the ways we work to the ways we play. And it even causes a number of social problems such as cloning humans.

      We have had lots of technology and it has changed our lives a lot. There is no doubt that humans will continue to use more and more technology. Here are some examples of modern technology that will change our ideas and will affect our lives greatly.

     Global positioning system (GPS) (全球定位系统)

      It's a system that uses radio signals from satellites to show exact information. It tells you where the user is on the earth in all weather conditions. It's made up of three parts: satellites, control equipments(设备) on land and receivers.

     Space Technology

      Russian and American scientists have worked together for the international Space Station (ISS) for a long time. They hope the ISS will provide a long-lasting lab. Such a lab will bring humans limitless (无限的) advantages. It's even hoped that one day space technology will take humans to their new houses in space.

     Underwater Robot

     Hercules is a kind of underwater robot with some high technology equipments. It will be used to look for ancient ships which were destroyed into the deep sea during their journey long ago.

     The world is changing so quickly that it's hard for us to catch up with all the new inventions because they seem to come out every month. It's important for us to learn about new technology and the role that it plays in our lives. So we should be willing to accept modern technology, or we will fall behind the times.