Critical Reasoning

A recent article in a literary journal argues that having a career separate from publishing makes writers more likely to produce large volumes of work. The article uses Anton Chekhov, a 19th century Russian writer who was also a physician, as the flagship example, tracing the roots of recurrent themes in his stories and plays to his experience in medicine. Anyone who writes, the article claims, will find his or her productivity vastly stimulated by work in another field.

Which of the following would provide the best piece of evidence for the claim made in the article?

A) An in-depth biography of a single writer, such as Chekhov, tracing the influence of a previous career on eventual literary output.
B) An interview with a panel of literary experts making the same claim.
C) A survey of the output of 100 writers, identifying those with highest output as the same ones with previous or separate careers.
D) A cross-reference of best seller lists from the last 20 years with a list of which of those writers had previous or separate careers.
E) An article by a psychologist discussing the emotional and intellectual factors involved in writing well.

the answer is not A but C, would love a good explanation