单选题 On Oct. 12, 1989, some Chinese scientists were working at the computers to look for the in- formation they needed. Suddenly they saw a lot of very bright spots crossing the computer's screens. At the same moment the computers were working much slower. To find out what was happening, they stopped their work to check some parts of the computers. To their horror, they found out that most of their stored information was got rid of by computer viruses (病毒). All these computers had been infected by computer viruses.
It is said that the computer viruses were made by a group of young men fond of playing tricks. They all have excellent education. They created the viruses just to show their intelligence. These kinds of computer viruses are named Jerusalem Viruses. These viruses can stay in computers for a long time. When the time comes they will attack the computers by lowering the functions, damaging normal programs or even getting rid of all the information.
We now come to know that Jerusalem Viruses often attack computers on Fridays and that they are spreading to a lot of computers. Among the countries that suffered computer viruses last year are Britain, Australia, Switzerland and the U. S.. But till now, how to get rid of the terrible viruses remains a problem.

单选题 The group of young men created the viruses to ______.

单选题 According to the passage, the underlined word "infect" in Paragraph 1 may have the same meaning as ______.

单选题 The viruses can cause all the following damages EXCEPT ______.

单选题 It can be learnt from the text that ______.