The answer to this question, ask yourself, "what was the author assuming in the argument that is suspect?" It seems that the author was assuming that computer use and television use were competing for the same hours in a person's life, so more of one means less of another.
Answer choice E suggests that maybe people are using computers more at work, a time when they can't really watch TV. If they increase computer use at work, then that would potential explain why they have not reduced their television consuming time.
You chose answer choice D, which confuses two different groups of people in the survey. Answer choice D implies that the author was originally assuming something about the number of respondents who reported 'spending increasing amounts of time per week using computers'. The author only made an assertion ABOUT those people, not about how many of them there would be, so evaluating the conjecture in D would not help you evaluate the argument.
