今年专四考试之后，我在第一时间分享了我的参考答案。大部分答案受到了广大考生的认可，但是语法和词汇部分的第一题的答案有一定争议，于是我们找到在美国的英语语言教学专家对此题做分析，下面是美国专家做出的回复：
　　let's talk about the no. 51 question.
　　In daily speaking , all 4 are acceptable. To choose the best ones, they are "who" and "that".
　　If we have to choose the best ONE, I believe that the correct answer is "that". 
　　One reason "that" may sound like the best choice is that it is often used. To avoid the choice between "who" and "whom", many speakers simply use "that" or "which".
　　As between "who" and "whom" in a sentence involving a linking verb such as "is" "are" "was" "were", I believe "who" is right because on one side of the linking verb is the subject and on the other side is a subject complement. The complement is not technically an object, and should therefore be in the subjective form. In other words, for a sentence such as "my uncle assisted the man () carried the toy car," the word should be "who" because "who" would then be the subject of "carry." But, for "my uncle assisted the man () the car carried," the word should be "whom" because the man would then be the object of the sentence "carry." There is no similar object-subject flip-flop for sentences with linking verbs. The two things on both sides are equal.
　　To sum up, "who" and "that" are both the right answer, but "that" just SOUNDS LIKE the better choice.
　　特别说明：由于一直没有找到今年的听力音频材料，所以暂时无法提供听力部分参考答案。