the actual statement is somewhat confusing/redundant so at least for me, it was important to boil it down to the two competing explanations that the question is referring to. what are they?
1) aging -> loss of creativity (scientists are not creative beyond 40)
premise: scientists are not creative once they reach 40
conclusion: aging causes loss of creativity
2) too long in one field -> loss of creativity
premise: by age 40, most scientists have been working in their field for a while
conclusion: working too long in one field causes loss of creativity
thus, the two competing factors that lead to loss of creativity are aging and working too long in one field.
we need an answer choice that deals with both of these. not one or the other. both.
a) entering a field at a considerably later age than common implies working for a shorter time in a field relative to other scientists. this statement links age and amount of time spent working in the field with creativity
b) weaker than above. doesn't seem entirely relevant
c) out of scope and only deals with (1)
d) deals with (2) -provides an explanation for why scientists would want to work for longer periods of time in one field, but does not help reconcile (1) and (2). this is also another statement that is plausible in the real world and makes sense, but its irrelevant here and most importantly does not deal with competing explanations
e) doesn't hep us....we can try and use this info. lets say that there is significant variation and some fields lead to more productive work then others. what does that tell us? how does that help us reconcile the "competing explanations"? it does not. this is also another likely-true-in-real-world-but-irrelevant type answer choice.
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