For centuries, the only form of written correspondence（通信）was the letter. Letters were, and are, sent by some form of postal service, the history of which goes back a long way. Indeed, the Egyptians began sending letters from about 2000 BC, as did the Chinese a thousand years later.
Of course, modern postal services now are much more developed and faster, depending as they do on cars and planes for delivery. Yet they are still too slow for some people to send urgent documents（紧急文件）and letters.
The invention of the fax（传真）machine increased the speed of delivering documents even more. When you send a fax, you are sending a copy of a piece of correspondence to someone by telephone service. It was not until the early 1980s that such a service was developed enough for businesses to be able to fax documents to each other.
The fax service is still very much in use when copies of documents require to be sent, but, as a way of fast correspondence, it has been largely taken the place of by email, Email is used to describe messages sent form one computer user to another.
There are advantages and disadvantages with emails. If you send someone an email, then he will receive it extremely quickly. Normal postal services are rather slow as far as speed of delivery is concerned.
However, if you write something by email, which you might later regret, and send it immediately, there is no chance for second thoughts. At least, if you are posting a letter you have to address and seal（封）the envelope and take it to the post box. There is plenty of time to change your mind. The message is think before you email!
25. We can learn from the text that________________.
A. the postal service has over the years become slower
B. email is less popular than the fax service
C. the postal service has over the years become faster
D. the fax service has a history as long as the postal service does
26. It can be inferred from the text that________________.
A. the fax machine was invented after the 1980s
B. letters have been used in China for about 1,000 years
C. the fax service had been fully developed by the 1980s
D. letters have been used in Egypt for about 2,000 years
27. In the last paragraph, the writer mentions “think before you email” to show that _________________.
A. you’d better not send your email in a hurry
B. you may regret if you don’t seal your envelope
C. you may regret before you send something by email
D. you need plenty of time to send an email
28. The text mainly deals with ________________.
A. the invention of fax machines B. the advantage of fax machines
C. the advantage of emails D. the progress in correspondence