Explanation

Reading the question: this question contains opinions, so we can digest it by finding and categorizing opinions. We've got a plan and a criticism of the plan, so there are two bodies of opinion: what the scientists think, and what the author thinks.

Creating a filter: more specifically, we are asked to weaken what the author thinks--we are weakening the criticism of the plan. The gist of this criticism is the second sentence; the final sentence is mostly puffery. The essence of sentence #2 is that, since emotional responses differ by geography, scientists will not find the causes of schizophrenia in a concentrated area. We could attack this view primarily by asserting that, even though emotional aspects of schizophrenia might differ by geography, the causes of schizophrenia don't. So we predict that the correct answer choice, a weakening statement, will be like, "even though emotional aspects of schizophrenia might differ by geography, the causes of schizophrenia don't."

Applying the filter: choice (A) is similar to our expectation, while choice (B) is not. Choice (C) is similar, but it fails to connect to or mention the causes of schizophrenia. Choice (D) weakens the wrong thing--it weakens the scientists' view that their plan will work. Choice (E) disputes the evidence, not the argument, and it doesn't dispute the evidence well, since it concerns adulthood and the evidence concerns childhood, presumably.

Logical proof: we are left with (A), which we can confirm through the negation test. If there are no common features linked to the causation of the disease, the scientists' plan would surely fail. Therefore, the statement in (A) is material to both the plan and the criticism of the plan. The correct answer is (A).