Recent evidence appears to contradict earlier findings that suggested

Pre-thinking:

The question stem asks us to select an answer choice that "provides evidence for determining whether physical fitness makes one react better to stress". Therefore, the correct answer option would likely have the following characteristics:

1) A scenario with stress and one without stress.
2) A group of subjects with and without physical fitness.
3) The reactions of the subjects to each scenario must unambiguously point to an answer to the question.

With this in mind, let us approach the answer choices.

(A) Superior reaction to laboratory stress situations was found to be more prevalent among women than among men. This does not factor in physical fitness in any way ie; (2) above is not satisfied. We are not concerned with the differences between men and women in reacting to stress.

(B) Healthy men, after training six months in weight lifting, encountered fewer potentially stressful situations in the subsequent six months. This option states that the subjects encountered fewer stressful scenarios. We can gauge the impact of "fitness" on "reaction to stress" only if we have both - this option does not tell us anything about the subjects' reaction to stress. (3) above is not satisfied.

(C) Subjects following a regimen during which they perfected their skills in a variety of relaxation techniques found that their lives seemed calmer after they began the regimen. This option provides a change in the "reaction to stress" (potentially, if we interpret the phrase "seemed calmer" as "better reacting to stress"). However, the regimen driving the change is on "relaxation techniques" and not "physical fitness". (2) above is not satisfied.

(D) College students with previous high levels of stressful life events showed a markedly reduced reaction to such events after training in aerobics for six months. All 3 points above are satisfied - correct answer.

(1) Situations with and without stress - "previous high levels of stressful life events ... such events after training".
(2) Subjects with and without physical fitness - "after training in aerobics"; the same group of subjects reacting differently makes the case stronger.
(3) Differing reactions - "showed a markedly reduced reaction"

(E) Subjects with a high level of self-esteem more often engaged in physical-fitness regimens than did a control group of subjects with average levels of self-esteem. This does not contain any information on the subjects' reaction to stressful events and hence does not provide any evidence to answer the question. (3) above is not satisfied.

Hope this helps.