Parents may be surprised at how fast their kids grow up，but a study finds that U.S teenagers are developing more slowly than those in the past.

Parents may be surprised at how fast their kids grow up，but a study finds that U.S teenagers are developing more slowly than those in the past.

（1）C.细节理解题。根据"Thewholedevelopmenthassloweddown.Today's18-year-oldsaremorelike15-year-oldsinthepast，"saidProfessorJeanTwenge."Teenagersaretakingfewerriskthanthoseinthepast.""整个发展已经放缓。现在的18岁少年更像过去的15岁少年，"让•特温格教授说。"青少年比过去少冒风险。"可知前两段告诉我们，现在的青少年相比过去很少冒险。故选C。（2）D.细节理解题。根据Oneofthereasonsforthesechangesisthattoday'steenagerswouldliketospendmuchtimeonline.TheykeeponwatchingvideosorplayinggamesontheInternetinsteadofspendingmoretimewiththeirfamilyandfriendsinperson.Anotheroneisthatparentshavebecomemuchmorechild-centric".Infact，parentshadbetterlettheirchildrendoeverythingbythemselves.Theyshouldtrytheirbesttomaketheirchildrenbecomeindependentassoonaspossible.变化的原因之一是今天的青少年喜欢花很多时间在网上。他们继续在网上看视频或玩游戏，而不是花更多的时间与家人和朋友在一起。另一个是父母变得更加以孩子为中心"事实上，父母最好让孩子自己做所有的事情。可知原因是ad两项。故选D。（3）C.文章结构题。文章第一段astudyfindsthatU.Steenagersaredevelopingmoreslowlythanthoseinthepast.提出现在青少年比以前的发展更缓慢，之后第二段和第三段提出了相应的依据，第四段则说明产生这个现象的原因，所以是总分总结构。故选C。（4）B.最佳标题题。根据文章第一段astudyfindsthatU.Steenagersaredevelopingmoreslowlythanthoseinthepast.提出现在青少年比以前的发展更缓慢，后文阐述了造成这个情况的依据和原因，可知全文都在介绍美国青少年的个人成长缓慢问题。故选B。