题干

下列关于基因工程及转基因食品安全性的叙述,正确的是(  )

A:基因工程经常以抗生素基因为目的基因

B:通过转基因技术可获得抗虫粮食作物,从而增加粮食产量,减少农药使用

C:通常用一种限制性核内切酶处理的基因,用另一种限制性核酸内切酶处理运载体

D:若转入甘蔗中的外源于自然界,则生产出来的甘蔗不存在安全性问题

上一题 下一题 0.0难度 选择题 更新时间:2013-06-27 03:22:23

答案(点此获取答案解析)

B

同类题3

阅读理解

    Last year my summer holiday was spoiled by my bringing along a modern convenience that was too convenient for my own good: the iPad. Instead of looking at nature, I checked my e-mail. Instead of paddling a small boat, I followed my Twitter feed(推特简讯). Instead of reading great novels, I stuck to reading four newspapers each morning. I was behaving as if I were still in the office. My body was on vacation, but my head wasn't.

    So this year I made up my mind to try something different: withdrawal from the Internet. I knew it wouldn't be easy, since I'm bad at self-control. But I was determined. I started by giving the iPad to my wife.

    The cellphone signal at our house was worse than in the past, making my at tempts at cheating an experience in frustration (沮丧). I was trapped, forced to go through with my plan. Largely breaking away from e-mail, Twitter and my favorite newspaper websites, I had few ways to connect to the world except for the radio—and how much radio can one listen to, really? I had to do what Ihad planned to do all along: read books.

    This experience has had a happy ending. With determination and the strong support of my wife, I won in my vacation struggle against the Internet, realizing finally that it was I, not the iPad, that was the problem. I knew I had won when we passed a Star bucks and my wife asked if I wanted to stop to use the Wi-Fi.“I don't need it,” I said.

    However, as we return to post-vacation life, a harder test begins: Can I continue when I'mback at work?

    There are times when the need to know what's being said right now is great. I have no intention of giving up my convenience completely. But I hope to resist the temptation to check my e-mail every five minutes, which leads to checking my Twitter feed and a website or two.

    I think a vacation is supposed to help you rest your brain to become more productive. Here I hope this one worked.

同类题5

 Are you a happy person most of the time? Or do you easily get angry sometimes? Everyone has a different temperament (脾气). It is usually believed that both genes (基因) and environment may affect people's temperaments in different ways. But now scientists have found that the season of birth also plays a role.

 Scientists from Budapest, Hungary, studied 400 university students. In the study, the students needed to finish a questionnaire (问卷). The purpose of it was to find out which of four kinds of temperaments they most had. From the questionnaire, scientists found that the students always answered something like "My mood often changes for no reason" and "I love to deal with new projects, even if it is risky". These answers were then matched with their birthdays.

  They discovered that people born in summer easily change between sad and happy moods compared to people born in winter. Those who always feel positive are mostly born in spring and summer.

The study also found that those born in autumn less probably had a mood of depression which may easily drive them to cry, while those born in winter were not easier to be angry.

 Scientists said that this was probably because the seasons had an influence on certain chemicals in the human body. And the chemicals are important to control people's moods even in adult life.

  ____________________________________________________________________________

"It seems that when you are born may increase or decrease your chance of developing certain mood disorders (紊乱)," lead scientist Xenia Gonda told The Telegraph.