E-mail is much ______than long-distance calling

1. A.
   cheaper
2. B.
   cheap
3. C.
   the cheaper
4. D.
   cheapest

E-mail is very popular today. People hardly post letters, _________?

E–book is short for electronic(电子) book. It is usually read on personal computers. Some mobile phones can also be used to read e–books.
Earlier e–books were written for a certain group of readers and were about only a few subjects. With the development of the Internet, knowledge and answers to a lot of questions mainly come from e–books. This is why the e–book business is increasing quickly.
E–books have many advantages. First, they save time. We don’t need to go a bookstore to buy books. Besides, we can find the topic we want to know about on the Internet, and then we can quickly get many e–books on similar topics. Second, e–books save money. Some e–books cost us little money, and there are millions of e–books on the Internet that we can get for free. Third, more trees are saved because e–books don’t need to be printed on paper. Fourth, e–books make reading more convenient. You can carry a whole library of hundreds of books with you in a small computer or any e–book reader(阅读器), without worrying about their weight.
But e–books have certain disadvantages. They need a personal computer or an e–book reader, and the information can be lost if its file format(文件格式) is not supported(支持) or changed in the reader’s computer.
However, e–books provide us with a new way of reading. That is good.
【小题1】Why is the e–book business increasing quickly? Because______________.