[解析]
(1)A 细节理解题,根据第二段And a teen's sense of self and values may be changed in a world where personal connections can be limitless,"said Sherry Turkle.可知研究人员认为青少年可能会产生不同的价值观,故选A.
(2)D 推理判断题,根据最后一段Teens say they feel good about what they say online or taking the time to think about a reply.Some teens admit that asking someone for a date,or breaking up,can be easier in message form,though they don't want to do so可知一些年轻人认为网上聊天可以帮助他们减轻他们的心理压力,故选D.
(3)D 推理判断题,根据第二段But researchers nationwide are increasingly worried that teens are becoming isolated第三段Another researcher,Robert Kraut,said he's worried about the"opportunity costs"(机会成本) of so much online time for youths可知作者通过这篇文章向我们介绍了关于青少年网上聊天的不同意见,故选D.
(4)B 主旨大意题,通读全文可知作者通过这篇文章向我们介绍了要注意青少年的使用电脑的习惯,故选B.