Communication via e-mail is by far the most common Internet activity. You can (71 ) with anyone in the world who has an Internet address or e-mail (72) with a system connection to the Internet. All you need is (73) the Internet and an e-mail program. Two of the most widely used e-mail programs are Microsoft’s (74) and Netscape’s Navigator. A typical e-mall message has three basic (75) : header, message, and signature.

（74）处填（）。

A. Yahoo

B. Explore

C. Foxmail

D. Outlook Express

活性炭用以去除水中的有机物，当碳的吸附能力饱和后，可以（）后重复使用

A.加热

B.反冲

C.再生

D.解吸