Read the following passage and mark the letter A, B, C or D on your answer sheet to indicate the correct word or phrase that best fits each of the numbered blanks.

          The Internet has rapidly developed and become part of (17)______ daily life. It's a very fast and convenient way to get information. People use the Internet (18) ______ many purposes: education, communication, entertainment and commerce. The Internet (19) ______ people communicate with friends and relatives by means of email or chatting. (20) ______, the Internet has limitations. It is time - consuming and costly. It is also dangerous because of viruses and bad programs. On the other hand, people (21) ______ use the Internet sometimes have to suffer various risks such as spam or (22) ______  junk mail and personal information leaking. So, while enjoying surfing, be alert.