【求助】关于比较结构中 助动词的添加的疑问

huhuaxiao123

Many teenagers undergo stress, but results of a recent study indicate that the patterns of stress that girls experience are more likely to result in depression than are those that boys experience.

(A) are those that boys experience
(B) what boys experience
(C) boys' experience would
(D) boys' stress patterns do
(E) stress patterns of boys

想问的是为什么those 前要加助动词are  
答案上提示防止歧义 但是没看懂怎么歧义

DUKB24

Many teenagers undergo stress, but results of a recent study indicate that the patterns of stress that girls experience are more likely to result in depression than are those that boys experience.

(A) are those that boys experience
(B) what boys experience
(C) boys' experience would
(D) boys' stress patterns do
(E) stress patterns of boys

想问的是为什么those 前要加助动词are  
答案上提示防止歧义 但是没看懂怎么歧义

-- by 会员 huhuaxiao123 (2012/10/24 15:57:44)

result in depression than (in) those(the patterns of stress)  that boys experience