Critical Reasoning

In many scientific disciplines, scientists generally do not do highly creative work beyond the age of forty, a tendency that has normally been taken to show that aging carries with it a loss of creative capacity. However, by the age of forty most scientists have been working in their chosen field for at least fifteen years, so an alternative explanation is that spending too long in a single field reduces the opportunity for creative thought.

Investigating which of the following would be most useful in choosing between the competing explanations described above?

A. Whether among those scientists who do highly creative work beyond age forty a large proportion entered their field at a considerably later age than is common
B. Whether scientists' choice of research projects tends to be influenced by their own belief that their most creative work will be done relatively early in their career
C. Whether scientists who are older than forty tend to find more satisfaction in other activities, such as teaching and mentoring, than they do in pursuing their own research
D. Whether funding agencies are more inclined to award research grants to scientists who are veterans in their field than to scientists who are relative newcomers
E. Whether there is significant variation among scientific fields in the average age at which scientists working in those fields are at their most productive

OA: A

Can someone explain?
I chose B instead of A....