It can be inferred from the passage that the most probable reason Scalp realistically describes the social setting in the majority of her novels was that she:
was interested in the effect of a person's social milieu on his or her character and actions
The author states that Scalp’s novels presented social settings realistically. The question asks why Scalp did so. Option (b) is the best answer. In the first paragraph, the author states that:“In her novels, Scalp is deeply engaged by the questions of how individuals are shaped (or deformed) by their social environments, how historical forces impinge on people’s lives, how class, wealth and gender help to determine people’s fates.” This shows that Scalp was interested in the effect of social environment on the individual.