问题 问答题

天然气输配,为什么要强调加臭?

答案

参考答案:

因为天然气本身是无色无味的,一旦泄漏在空气中很容易达到爆炸极限遇火发生爆炸危险,如果按规定标准加臭后,一旦空气中天然气浓度达到爆炸极限的20%时人就可通过气味觉察,从而及时采取安全防范或检查措施,杜绝事故的发生。

单项选择题

How to protect children Web fans from unsuitable material on-line while encouraging them to use the Internet has long been discussed in the US.

For some parents, the Internet can seem like a jungle, filled with danger for their children. But jungles contain wonders as well as dangers and with good guides, some education, and a few precautions, the wilds of the Internet can be safely navigated. "Kids have to be on-line. If we tell our kids they can’t have access to the Internet, we’re cutting them off from their future, " said an expert.

Most kids have started to use search engines. Many of them are great for finding tons of interesting Internet sites, and they can also locate places where you might not want your kids to go. There are search engines designed just for kids. A certain software contains only sites that have been selected as safe. The most popular way to limit access would be to use what is known as a "content screener". But this can’t be wholly reliable, and the best thing parents can do is to talk to their kids and let them know what is OK or not OK to see or do on the Internet. Another way is that mum or dad is nearby when the child is surfing the Internet.

A few other tips

·Don’t put the PC in a child’s room but keep it in an area where mum or dad can keep an eye on things. That also makes the Internet more of a family activity.

·Ask your child what he or she has been doing and about any friends they make on-line.

·Tell your child not to give on-line strangers personal information, especially like address and phone number.

·And tell your children never to talk to anyone they meet on-line over the phone, send them anything, accept anything from them or agree to meet with them unless you go along.

The passage is mainly about the subject of()

A. American children going on-line

B. Internet in America

C. appreciating Internet

D. opposing children’s on-line

单项选择题