Computers tend to perform tasks more slowly after two

Computers tend to perform tasks more slowly after two years of use. One software designer believes that viruses, and not compatibility problems, are the primary cause of this phenomenon.

This question essentially asks us to choose a line of inquiry that would yield relevant information—information that would make it either more or less likely that viruses are responsible for the fact that computers slow down after two years of use.

Notice that only the inquiry described in answer choice B would provide information that either supports or undermines the conclusion. If infecting a computer with a virus will cause it to run more slowly, then it is more likely that viruses are responsible for slowing down older computers. If infecting a computer with a virus will not cause a computer to run more slowly, then it is less likely that viruses are responsible for slowing down older computers.

Answer choices A, C, D, and E each describe inquiries that would yield irrelevant information. For instance, suppose that the inquiry in answer choice A reveals that Apple computers are more likely to slow down than Dell computers. So what? That additional information would tell us nothing about whether viruses are responsible. Therefore, knowledge of the computer manufacturer's name is irrelevant to the argument.