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.
（72）处填（）。
A. account
B. No
C. user
D. administrator
