I believe it is D use an outline: does not have to do with gathering info for a problem- solution essay.
Although for gathering info- surveys, in-depth interviews, and cities examples are primary research that are useful and valuable info. as it surveys people.
Hope this helps :)
The correct answer should be a. past participle, if you are referring to the verb "hung". This is because only past participles can form present perfect or past perfect and "had hung" is a past perfect form.