Answer choice "A" strengthens the conclusion that the fruits cause atypical Parkinson's because when the proposed cause (the fruits) were removed, the effects (Parkinson's symptoms) were abated. This indicates a causal link.
Answer choice "D" would actually weaken the researcher's proposal that the fruits cause the atypical Parkinson's. In answer choice D, there are 10 healthy adults who are experiencing MORE of the proposed cause (fruits) and none of the effect (Parkinson's.) This indicates that there is no causal link between the fruits and the illness.