The correct answer is B. often affect the way a story is told.
An author's historical background is very important because his (or her) ideas and the way of writing will be affected by his/her real life. If an author is living in the Victorian age, their style of writing as well as themes will usually be suitable for the era they are living in.
So A is definitely incorrect because the impact is huge. C is incorrect because it is really easy to determine the historical background based on many clues. D is incorrect because the plot may also be affected by the historical era.