deal不是purchase的同位语，purchase只是deal的一部分，买和卖 共同构成deal

E The fact is wordy; the inverted construction
does not successfully convey the meaning of
the sentence.

A 主语和宾语都是从句，GMAC觉得不好
A Inverting the usual order results in an
ungrammatical construction in which the
main verb is both preceded and followed by
a subordinate clause.

平行

mark。表目的时用of doing的情况。

逻辑连词重复。错选E。
mark所有格定语和名词定语的区别。

E. This version is wordy and repetitive (possible and could repeat the same meaning);
because the antecedent for its is so far from the opening phrase, the reference is
unclear.

我晕，一直以来so...that...就是指太怎么样以至于怎么样，变成so...as to...真的很难以接受啊。还有d选项，有enough to do 足以xx去做什么，就可以有enough not to do 足以xx不去做什么，跟因果关系是有啥联系啊？

mark。破折号

In this sentence the pronoun it does not always refer to condition, but, for the sake
of clarity and correctness, it should. Detect a condition when it is present is correct
and should be followed by a corresponding construction: indicate that it is present
when it is not. The construction of there is one leaves it without a referent.

A There is one leaves it in the final clause without a referent.
B Detect a condition is more precise because it emphasizes the condition
itself; there is one leaves it without a referent

C Correct. The three uses of the pronoun it refer clearly to condition, and
the two parts of the sentence correspond.
D When a condition is present emphasizes the time of the detection rather
than the condition itself. The final it has no referent.
E Presence illogically repeats the same idea as when it is there. The final it
has no referent.

mark。某人通过一个“媒介”来做某事的，都被认为是“媒介”发出的动作，即，以最终发出动作的名词为标准。

E选项：brighten和knock out都应是trigger的伴随状语，两者应该保持语法上的平行。

Point to discuss:
As per https://www.manhattanprep.com/gmat/forums/painted-caves-at-lascaux-and-altamira-t7994-15.html
"what his father gave him are a few books."
Ron: "no, you would still write "is", because the subject of the verb is still what his father gave him, not a few books."

The subject here is “what is much more difficult to determine”
As per Manhattan SC guide this is called Sub Phrase and it is always singular.

D. This version is wordy and confusing because of the sequence of relative clauses
beginning with that.

as an adjective, 15 years
becomes 15-year.

AD 纠结 D. The is omitted before three.

The idiomatic expression established . . . as is preferable
to the nonstandard and somewhat unclear established . . . to be.

地点啊时间啊介词短语跟在一个名词后，会让人觉得修饰这个名词；

补充一点：强调句强调时间状语Or地点状语，貌似也是用that；没有用when 或者 where，个人感觉，没查证过