The way to evaluate D is to consider the following.

The prompt talks of the results of making the information available.

If the answer to D were "Yes" then one might think that the results of the government plan would be limited to nonexistent, because other websites already provide the same information, and one might reasonably question whether providing information that is already provided would make much difference. (Note, choice D is not well written and does not clearly say that the other sites would provide information the same as what the government plans to provide, but I am going with the idea that that interpretation is in line with what was intended by the writer of the question.)

So D may seem to be useful in evaluating an argument about the results of the plan.

At the same time, this question is not about the DEGREE to which the plan will have results. This question is about the NATURE of any results of the plan. In fact, we would not really change the conclusion were we to rewrite it as, "While the intentions are good, the results, to the degree that there are any, might just be the opposite."

So D, the answer to which may affect the degree to which the plan has results but not the nature of any results of the plan, is irrelevant.

C, on the other hand, is helpful in evaluating the argument, because if the answer to C were "No," then, even without the salary information, the students would already be not taking their passions into account in making school choices, so their basing their choices on the salary information would not cause the effects described in the argument.

The correct answer is C.