21. By saying “... owners of well over half of all World Wide Web sites have set up home without fitting locks to their doors" (Lines 3-4, Para. 2), the author means that _____. (A) those happy times appear still to be with us (B) there simply wasn't any crime to worry about (C) many sites are not well-protected (D) hackers try out tricks on an Internet site without actually breaking in

22. SATAN, a program designed by Dan Fanner can be used ____________. (A) to investigate the security of Internet sites (B) to improve the security of the Internet system (C) to prevent hackers from breaking into websites (D) to download useful programs and information

23. Fanner's program has been criticized by the public because . (A) it causes damage to Net browsers (B) it can break into Internet sites (C) it can be used to cause disorder on all sites (D) it can be used by people with evil intent

24. The author's attitude toward SATAN is _____. (A) enthusiastic (C) positive (B) critical (D) indifferent

25. The author suggests in the last paragraph that . (A) we should make full use of the Internet before security measures are strengthened (B) we should alert the most influential businessmen to the importance of security (C) influential businessmen should give priority to the improvement of Net security (D) net inhabitants should not let security measures affect their joy of surfing the Internet