题干

在下列描述中,错误的是                                                                       (   )

A:核酸是一切生物的遗传物质

B:能发生碱基互补配对行为的细胞器有线粒体、叶绿体、核糖体

C:种内斗争,对于失败的个体来说是有害的,甚至会造成死亡,因此对于整个种群的生存也是有害的

D:高度分化的植物细胞仍然具有发育成完整植株的能力,也就是保持有细胞全能性

上一题 下一题 0.0难度 选择题 更新时间:2011-03-31 01:06:02

答案(点此获取答案解析)

C

同类题2

阅读理解

    Well, parents, surprise! Lots of us are using Twitter and Facebook to thumb rides, and not just to school. It's awkward to be refused when you call a friend and ask for a ride. But with Twitter, you just look for other people heading the same way.

    It may sound risky, so many teens stay within their own social circles to find rides, and don't branch out beyond friends when asking on Twitter just like me, but to some young people, especially those taking longer trips, stranger danger is less of a concern.

    “I think the digital connection of young people is really important, because younger generations grew up sharing things on line, sharing files, photos, music, etc, so they've been very used to sharing,” said Juliet Schor, a sociology professor at Boston College.

    The sharing economy got big during the recession (经济衰退), allowing people to access more goods, services using technology and even to share costs. And that technology, for me, is what the car was for my mom, a gateway to more freedom, like what my friend Earl says, “The symbol of freedom isn't the car any more because there's technology out there connecting you to a car.”

    According to the researchers at the University of Michigan, 30 years ago, eight in ten American 18-year-olds had a driver's license compared to six in ten today. So it's not that surprising that on my 16th birthday I wasn't rushing to get a license but an iPhone.

“Driving, for young people, does mean they have to disconnect from their technology, and that's a negative. So if they could sit in the passage side and still be connected, that's going to be a plus.” Schor continued.

    To me, another plus is that ridesharing represents something, something much bigger than trying to save money. I see it as evidence that people still depend on each other. My generation shares their cars and apartments the way neighbors used to share cups of sugar. For the system to work, some of us still need our own cars. But until I get my own version of the silver Super Beetle, you can find me on Twitter.