A new diet regimen encourages daily consumption of a specific probiotic supplement. Proponents claim that this regimen significantly boosts the immune system, citing a study where participants on the diet exhibited higher levels of T-cells, crucial components of immune response. However, critics argue that the study is flawed because participants were also advised to exercise regularly, a known immune booster.
Correct: C
The critics argue that the observed increase in T-cell levels might be due to exercise, not the probiotic supplement. To strengthen the proponents' claim that the probiotic is responsible, one must eliminate or significantly reduce the alternative explanation provided by the critics. Option C does exactly this: if a control group that *only* exercised (without the supplement) showed no significant T-cell increase, it directly refutes the idea that exercise alone caused the T-cell boost, thereby strengthening the conclusion that the probiotic is the causal factor. Option A does not eliminate exercise as a factor; it only states that more rigorous exercise didn't yield *greater* increases. Option B suggests a potential flaw in the study, which would weaken, not strengthen, the claim. Option D is irrelevant to the core argument about exercise versus the specific probiotic. Option E introduces another potential confounding factor (restriction of processed foods), which would suggest something *other* than the probiotic could be responsible, thereby weakening the claim.