The argument says that most research scientists do their best work before the age of 40. Many assume the reason is that as scientists age they become less creative.
The argument proposes another explanation: scientists exhaust their creative opportunities after 15 years, which, for many, is by the time they reach 40.
A finding supporting this second explanation could focus on the majority of scientists. But such an answer choice would be restating the argument, e.g. most scientists who worked in the field for fifteen years report being less creative.
Instead, the correct answer (B) focuses on those scientists who do creative work after age 40. If they started their careers later in life, they have yet to exhaust their creative opportunity for creative work.
Answer choice (D) also focuses on the over 40 cohort. However, the focus is not research and the amount of time they have been doing creative work in their respective fields.
Instead (D) focuses on satisfaction. Nowhere does the argument make a connection between the quality of work done and the satisfaction gained from it.
For example, imagine a scientist who entered the field later in life. Over 40, he tends to enjoy teaching more than research. Yet, because he entered the field late, he has yet to exhaust his opportunity for creative work. He may not enjoy this work as much as teaching, but this predilection doesn’t preclude him from doing creative work after 40.
Magoosh Test Prep