Nowadays, more and more people like to shop on the Internet.  How can you protect yourself from different types of Internet tricks?  Following these tips can make you online shopping safer：
    (1) Never click on an unsolicited(主动提供的) e-mail.  If you are interested in the things well-known company that sells the same thing, don't click on any links in the e-mail itself.
    (2) Don't answer any e-mail that asks you for personal financial(财政的) information.  Most of the legitimate(合法的)companies will not ask your information through e-mail.  And don't believe what the e-mail says easily.  Sometimes some e-mail will ask you to make a telephone call to get more information about the things you want.  Don't forget to check the phone number on your phonebook to make sure it is the number of a legitimate company before you make the call.
    (3) When you are searching for information on the Internet, make sure that there is a key symbol at the bottom of your browser(浏览器)and the “http” in the website address.  These mean that the website is safe.
    (4) Don't sent your money to an unknown website before you receive the things they send to you and make sure they work well.
    Shopping on the Internet is convenient and fun.  It is also safe if you are careful enough.

This morning I have         art lesson, and art is         easy subject.

请在下面的数字后面填上适当的单位：

一名中学生的质量约是50____ ；

一根头发的直径是：70____ ．

已知a，b两数在数轴上的位置如图所示，则化简代数式|a+b|﹣|a﹣1|+|b+2|的结果是（　　）