CEO: Over the past several years, we have more than doubled our revenu

This is a "weaken the plan" type weaken question. In plan-style critical reasoning questions, view the steps of the plan as the premises and the ultimate objective of the plan as the conclusion. Here the step is to increase the interest rate charged on outstanding balances, and the goal is to increase profits. Because we are weakening, we are looking to insert another premise that would attack the gap between this premise and conclusion.

Answer choice A is out of scope and irrelevant. We are focused only on this one company, not others.

Answer choice B is a common trap answer to these style questions. The presence of a better plan does not weaken the existing plan; it is out of scope.

Answer choice C is also out of scope. Discussing how the problem may resolve itself does nothing to attack the gap between premise and conclusion in this plan.

Answer choice D is strengthening the argument, and is thus a strengthen trap answer to a weaken question.

Answer choice E nails it and is thus correct. If the increased APR will worsen the default situation (which is what the CEO is trying to account for by increasing the APR), then it is very possible that the goal of increasing profits will not be accomplished. The company may actually end up decreasing profits even further, or remaining steady.

I hope this helps!