[求助]请教几道题目

1. According to a study published by Dr. Myma Weissman, only one percent of American born before 1905 had suffered major depression by the age of seventy-five; of those born since 1955, six percent had become depressed by age twenty-four.

(A) only one percent of American born before 1905 had suffered major depression by the age of seventy-five; of those born since 1955, six percent had become depressed by age twenty-four

(B) only one percent of American born before 1905 suffer major depression by the age of seventy-five; if they are born since 1955, six percent become depressed by age twenty-four

(C) of American born before 1905, only one percent of them have suffered major depression by age seventy-five, but six percent of those born since 1955 do by the age of twenty-four

(D) major depression is suffered by the age of seventy-five by only one percent of Americans born before 1905, and by age twenty-four by the six percent born since 1955

(E) Americans born before 1905 suffer major depression by the age of seventy-five only one percent of the time, but six percent of those born since 1955 did so by age twenty-four

“of those born since 1955, six percent had become depressed by age twenty-four”

总觉得这句话有问题

2. It is an oversimplified view of cattle raising to say that all one has to do with cattle is leave them alone while they feed themselves, corral them, and to drive them to market when the time is ripe.

(A)   all one has to do with cattle is leave them alone while they feed themselves, corral them, and to

(B)   all one has to do with cattle is to leave them alone to feed themselves, to corral them, and

(C)   all one has to do with cattle is leave them alone while they feed themselves and then corral them and

(D)  the only thing that has to be done with cattle is leave them alone while they feed themselves, corral them, and

(E)   the only thing that has to be done with cattle is to leave them alone while they feed themselves, to corral them ,and

“all one”怎么解？ “is leave” 又是怎么回事？

3. While all states face similar industrial waste problems, the predominating industries and the regulatory environment of the states obviously determines the types and amounts of waste produced, as well as the cost of disposal.

(A)   all states face similar industrial waste problems, the predominating industries and the regulatory environment of the states obviously determines

(B)    each state faces a similar industrial waste problem, their predominant industries and regulatory environment obviously determines

(C)   all states face a similar industrial waste problem, their predominating industries and regulatory environment obviously determines

(D)   each state faces similar industrial waste problems, the predominant industries and the regulatory environment of each state obviously determines

(E) all states face similar industrial waste problems, the predominant industries and the regulatory environment of each state obviously determine

请以后问题分贴。每个帖子一旦超过2题，让人头昏。

1，of those born since 1955, six percent had become是可以的， of those born since 1955, six percent of them had become不可以。

2，what sb has to do is (to) do, all sb has to do is (to) do. 如果类似的主语从句中的谓语动词是do，主句的作表语的不定式可以省略to。

3，E，主谓一致。