Complete Question Explanation
Point at Issue. The correct answer choice is (D)
Wirth clearly would agree with answer choice (A). Chang's opinion is more difficult to establish. Remember that Chang did say, "I do not dispute your evidence." This means that he agrees that no evidence has been found to prove that a single gene is responsible for predisposing people to manic-depression. Chang also states that researchers have "found evidence that a set of several genes is involved," but this implicitly indicates that they have only found evidence of interaction, not actually identified the genes themselves. Thus, Chang would be forced to agree with answer choice (A). Since both agree, answer choice (A) must be incorrect. Answer choice (B) is incorrect because both would probably disagree with the statement it contains.