Why is studying an author's culture important?
a. to the reader understand the use of figurative and connotative language in the story
b. to the reader understand how the characters are able to overcome the story's conflict
c. to the reader understand the quality of the writing and the author's level of education
d. to the reader understand the underlying values and beliefs of the characters

(the answer is d)

The answer is D.

Culture refers to a particular ‘way of life’ (experience), involving religion, race and nationality, as well as things like food, dress code and manners. Literature has been defined as "the human experience."  It is the outpourings of the artist's heart and soul.  To know about the personal background of this artist, therefore, only makes sense. For example Ernest Hemingway in "A Farewell to Arms" , his experience are in the background of this novel.

A - I wish he were more prolific.

The past tense verb for to be is were/was. Seeing as there are only two answers that include that(A and C), it will narrow down the choices.

The subjunctive mood is used to express wishes and hypothetical situations.

(e.g. If I were in your place, I would not do it.)

Seeing as C does not express a wish, demand, or a hypothetical situation, the answer is A.