错选D，犯了整体和部分的错误。

这是排列组合里的排列，看顺序的。

P(3,3)*1/3^3

这个数必须是Prime number的平方；两个Prime number的乘积至少会有四个factors

老师，可否解析一下A和D选项，对Three out of every four automobile owners来说，是用谓语单数还是复数？为什么是own a bicycle，bicycle为什么不用复数？

The Hopis' retention of their distinctive sociocultural system has been attributed to the Hopi religious elite's determined efforts to preserve their religion and way of life, and also to a geographical isolation greater than that of many other Native American groups, an isolation that limited both cultural contact and exposure to European diseases.

in this case, the given scientific name (Confuciusornis sanctus) is just an additional, disposable fact, and so is written as an appositive modifier.

You're looking for idiomatic usage that agrees with 'risk', not 'chance'.
例句as small a collection as three pirated albums has occasionally drawn the attention of the recording industry.
in this case, 'collection', not 'albums', is the subject of 'has drawn' (which can be inferred from the fact that 'has' is singular).

这里的方法是叫“取非”吗？

With MOST adjectives, it's ok to write "NOUN as ADJ as..."
E.g., Women as beautiful as my wife are rare.

On the other hand, if the adjective is "many", "few", "much", or "little", then you cannot write "NOUN as ADJ as..."
Instead, you must write
as many NOUNs as...
as few NOUNs as...
as much NOUN as...
as little NOUN as...

rally有止跌回升的的意思

You don't need an actual past-tense verb. You just need a clear indicator of a definite point in the past——the point that serves as the point of view for "had ___ed".

Ron D:, this choice has an -ING modifier modifying another -ING modifier. i don't think that's a legitimate structure; at the very least, i have certainly never seen it in any halfway legitimate official sentence.

E： It is important to note that the fact that United States bought Louisiana for about four cents an acre had no bearing (was not the reason) on doubling the country's size and bringing its western border within reach of the Pacific Ocean.

终于完全分析对一次了

这道题有点意思，Ron在论坛上把OG的解释骂了一遍，说写OG的人不是出题的人，GMAC把OG的撰写工作外包，因为外包便宜，GMAC出题的全明星团队（all-stars），不参与OG题目的解释，OG上面充满了解释错误，哈哈。这道题的“比较”不是出题点，所以 A，B，C的前半句比较都没问题，我同意Ron，问题在句子后面的结构。大家可以谷歌一下这道题。

老师，在您的书P88 的例句中 “Gas prices were higher in 2002 than in 1992” 的解释里提到 虽然这比较的是两个时期的油价，但也可以比较两个时期汽油价格的情况，所以in 1992可以算作是比较的部分。

所以这道题并不需要知道a的值是多少？

读题失败：读成the tip driver charge George了

B选项错在over membership in the tailors' guild。我的理解是因为女裁缝协会的存在，威胁到男裁缝请家里的女裁缝干活、作老大的权利，而不是纠结于 membership in the tailors' guild