平行原则要求在GMAT中如果有连词以及短语来引导元素，比如 X and Y， both X and Y either X or Y等, X和Y必须保持形式的一致性。这些结构很容易被学生发现，学生只要能发现平行问题，还是非常容易去解决的。
eg：
Recently physicians have determined that stomach ulcers are caused not by stress, alcohol, or rich foods, but by a bacterium that dwells in the mucous lining of the stomach.
Not X but Y， 这句话中X Y都是 by sth 的形式，所以是平行的。
这样看平行结构真的不难，只要我们仔细一点肯定能比较出X和 Y哪个选项是一致的形式。但是GMAT为了能够难倒我们，真是要煞费苦心：出题者往往通过句子的复杂性来隐藏平行结构，出题者还是会用到障眼法，不会把平行的元素都放到划线中，而是只放其中一个元素，其他的元素都在未划线中，所以只关注划线部分的小伙伴就会发现无法判断划线中那个X的形式到底该是如何了！！
The Act enables the United States Trade Representative to single out a country as an unfair trader, begin trade negotiations with that country, and, if the negotiations do not conclude by the United States government's being satisfied, to impose sanctions.
如果只关注划线部分，我们就被蒙蔽了！根本不知道 to impose对不对。这句话中三个动词进行平行,可是第三个元素是在划线中的，必须意识到三个动词形式是一致的，前两个single out, begin 在未划线部分中使用的是动词原形，所以划线中的impose也必须是动词原形才能一致啊！！故 to impose是错误的。
准备好了吗？我们实战演习OG一道题：
In a plan to stop the erosion of East Coast beaches, the Army Corps of Engineers proposed building parallel to shore a breakwater of rocks that would rise six feet above the waterline and act as a buffer, so that it absorbs the energy of crashing waves and protecting the beaches.
(A) act as a buffer, so that it absorbs
(B) act like a buffer so as to absorb
(C) act as a buffer, absorbing
(D) acting as a buffer, absorbing
(E) acting like a buffer, absorb
看到五个选项的变化，选项区别在哪里呢？ act VS acting absorb VS absorbing 到底该用何种形式呢？好纠结。如果我们仅仅就盯着五个选项研究下去是没有结果的。必须用于探索发现啊！
The Army Corps of Engineers proposed building parallel to shore a breakwater of rocks that would rise six feet above the waterline and act as a buffer, so that it absorbs the energy of crashing waves and protecting the beaches.
没错！！发现了两个平行标志AND,突破划线从整个句子来看，划线中的act是和前面的 rise 平行的！！而划线的absorb是和后面的protecting平行的，这道题考察了两次平行！！所以 act必须和rise形式一致都是原形，absorb要和后面的absorbing形式一致，必须也是absorbing的形式！！！这样排除只能选择C，done！！！
由于这点非常重要，我们再来体会一下出题人的障眼法！！这道题难度再次升级，平行的不再是一个动词了！！
Based on records from ancient Athens, each year young Athenian women collaborated to weave a new woolen robe that they used to dress a statue of the goddess Athena and that this robe depicted scenes of a battle between Zeus, Athena's father, and giants.
(A) Based on records from ancient Athens, each year young Athenian women collaborated to weave a new woolen robe that they used to dress
(B) Based on records from ancient Athens, each year young Athenian women had collaborated to weave a new woolen robe with which to dress
(C) According to records from ancient Athens, each year young Athenian women collaborated to weave a new woolen robe that they used to dress
(D) Records from ancient Athens indicate that each year young Athenian women collaborated to weave a new woolen robe with which they dressed
(E) Records from ancient Athens indicate each year young Athenian women had collaborated to weave a new woolen robe for dressing
这道题划线部分比较长，句子最开始的表达形式不一，有什么区别呢？想不出来。。。再看到collaborate时态不一样，想不出来。。。宾语后面定语从句形式不一样，还是想不出来。。。What should we do!!! 如果这样想下去我们正好是被出题者的障眼法所击败了！！
我们要从全局把握句子，我们要注意未划线部分中的 and that从句！！既然有and that，那么前面一定有个that从句！！前面用到that的是 A C D选项。再次我们注意到 A C是定语从句的that，而D是宾语从句的that。我们看未划线部分that this robe depicted scenes of a battle between Zeus, Athena's father, and giants. 这that从句是完整的，不可能是定语从句，所以排除AC 选择D。这道题设置的还是非常有技巧的，也是很容易让学生忽略这里两个宾语从句平行的现象。
Records ……indicate that……and that…….
练习题：
In late 1997, the chambers inside the pyramid of the Pharaoh Menkaure at Giza were closed to visitors for cleaning and repair due to moisture exhaled by tourists, which raised its humidity to such levels so that salt from the stone was crystallizing and fungus was growing on the walls.
(A) due to moisture exhaled by tourists, which raised its humidity to such levels so that salt from the stone was crystallizing
(B) due to moisture that tourists had exhaled, thereby raising its humidity to such levels that salt from the stone would crystallize
(C) because tourists were exhaling moisture, which had raised the humidity within them to levels such that salt from the stone would crystallize
(D) because of moisture that was exhaled by tourists raising the humidity within them to levels so high as to make the salt from the stone crystallize
(E) because moisture exhaled by tourists had raised the humidity within them to such levels that salt from the stone was crystallizing
解析：
平行的是由so…that引导的两个结果状语从句，已经把未划线的平行部分标出来了。。。。
