With reading comprehension questions that ask us for the primary purpose of the passage, it helps to have a prediction in mind before looking at the answer choices.
From reading the passage, we know that the main purpose is to tell the land managers that they way they're managing wildfires is not good and that there is a better way they could mitigate the risk of uncontrollable wildfires. In the answer choices, we're looking for an answer that paraphrases the prediction we've made.
(E) states that the main purpose of the passage is to argue that two seemingly contradictory goals of a policy are actually compatible in a fundamental way. Where are the contradictory goals? They're not present in this passage. Also, this answer choice does not match our initial prediction of what the primary purpose of the passage is. We can eliminate this answer.
(D) is just what we're looking for. It captures the author's discussion of evidence against the current policies in controlling wildfires and mentions the policy change (discussed in the third paragraph) that the author supports. This is our answer.
Hope this helps. Let us know if you have more questions!