84. One legacy of Madison Avenue's recent campaign to appeal to people fifty years old and over is the realization that as a person ages. their concerns change as well.

(A) the realization that as a person ages, their

(B) the realization that as people age, their

(C) to realize that when a person ages, his or her

(D) to realize that when people age, their

(E) realizing that as people age, their

In choice A, the plural pronoun their does not agree in number with the singular noun person. Choices C, D, and E can be faulted for failing to complete the construction One legacy ... is with a noun that matches the noun legacy; these choices use verb forms--the infinitive to realize or the present participle realizing--in place of a noun such as realization. Further, when in C and D is less precise than as in characterizing a prolonged and gradual process such as aging. B is the best answer.

D为什么不对，名词必须用名词对应，但是动词不定式也可以做名词啊

请指点

还是那个结构：

A is B, A acts as B这样的结构，A和B的逻辑对称很重要。

One legacy不是 to do sth, 而是sth