陈向东的一道逻辑请教

1．        Although the ratio of physicians to totoal   population is about the same in the united states and Canada,the United States has 33 percent more surgeons per capita.Clearly,this is the reason that people in the United States undergo 40 percent more operations per capita than do Canadians.
The explantion given above rests on which of the following?
A the patients in the United States do not have a greater need for surgery than do patients in Canada
B the population in the United States is not larger than that of Canada
C United States sometimes travel to Canada foe certain kinds of surgery
D generated practitionsers is a candidate for surgery before sending the pateint a surgeon
E there are no unneseccary surgical operations performed in  Canada

这题答案为A,我觉得这题主要是把 他们之间的关系用比例列出来,但是我不会列出内部关系?请教大家以下,谢谢

 

此外,一道OG上的语法题不是很明白,

In virtually all types of tissue in every animal species dioxin induces the production of enzymes that are the organism's attempt to metabolize ,or render harmless,the chemical irritant.我对划线部分不明白，为什么会有ＴＨＥ　呢？因为HARMLESS 是形容词，应该与后面ＣＨＥＭＩＣＡＬ　一起修饰ＩＲＲＩＴＡＮＴ。

请大家帮忙指点一下，我是才开始看ＧＭＡＴ一星期，报名在６月份，现在基本上天天看逻辑，因为这部分实在很差，还没有很多大牛的　那种做逻辑的感觉，也很焦急呀。