You've found an article in the readers' guide that you want to locate. what information would be least important in finding it?
a) title of the article
b) volume & page number
c) author's name
d) subject heading

The correct answer is option D) "Subject heading". Since the main purpose is to locate an article in the Readers' Guide, the information of subject heading is the least likely that would help to achieve this purpose. Subject headings are useful to find articles regarding a particular topic, but if you already found the article and the idea is to locate, subject heading is not useful.

it translates into:

read the letter of your pen pal. write and answer 3 questions.