亮亮和田田两位同学欲测一段铁路的长，但没有合适的刻度尺，他们知道声音在空气中的传播速度为340m/s，在钢铁中的传播速度为5000m/s，于是亮亮站在欲测铁路的一端，田田站在铁路的另一端，亮亮用锤子敲击一下铁轨，田田听到了两次响声，两次声响的时间间隔为2s，这段铁路大约有多长？

种子比孢子的生命力强，是种子植物更适于陆地生活的重要原因。

    Are children becoming addicted to the Internet?

    Children are becoming addicted to the Internet and for many it is one drug that can't be beaten. Not all children, but an alarming number of them are being swept up in this age of digital information.

    Websites like Myspace, Youtube, and Facebook, are becoming so popular that many kids can't help but to be addicted to them just in order to fit. Why not become part of a society where you judged by how many friends on a friend list ? What has become of the world , when instead of calling your best friend on the phone you send them a message electronically and wait around for hours to see if they get on and read it ?Often on the web there just aren't enough adults setting kids straight and too many teenagers causing trouble .

    However, it is biased to claim all kids are addicted, or even that all kids who are addicted to the web are negatively affected by it. While the web can be a large waste pool of negative influence, it is also a wealth of positive knowledge, friendly social networking, and even gateways to future employment. Perhaps it isn't so important whether or not a child is addicted to the web and more important that parents know exactly what the kids are doing there.

    Many computers have optional parent controls that allow parents to block the children from entering certain types of sites, or even individual ones. Such programs are unfortunately not used enough by today's parents, who in many cases are caught up on computers themselves. All one needs to do is google search parental controls and you will be provided with any number of companies that can help with programs for tracing child activity and, if necessary, limit time spent on the Internet .

世界人种、语言、宗教与其主要分布区相符的是（　　）