我們在 OG 裡面，常看到一個名詞: parallel reasoning，那到底什麼是 parallel reasoning (平行推論) 呢?
在這裡，我稱 support 有兩種情況為 parallel reasoning
1. 完全相反的因果關係: 例如 A = B, -A = -B 就可支持
For example:
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When feeding, aquatic birds known as phalaropes often spin rapidly on the water’s surface,
pecking for food during each revolution. To execute these spins, phalaropes kick one leg
harder than the other. This action creates upwelling currents. Because plankton on which
phalaropes feed typically occurs in greater quantities well below the surface, it is
hypothesized that by spinning phalaropes gain access to food that would otherwise be beyond
their reach.
Which of the following, if true, most strongly supports the hypothesis?
A. Phalaropes rarely feed while on land.
B. A given phalarope spins exclusively either to the right or to the left.
C. Phalaropes sometimes spin when they are not feeding.
D. Different phalaropes spin at somewhat different rates.
E. Phalaropes do not usually spin when food is abundant at the surface.
Ans: E
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題目的因果為: birds spin --> access to food
而答案 E 是說 birds not spin --> no need for access to food
這就是一個相反的因果關係
2. 不同例子出現相同的因果關係: 在 CR 錯誤答案答案之中，最多的錯誤原因為"無關 (irrelevant)。但有時，答案卻可以出現完全沒出現過的對象。那是因為當有個不同的例子，其因果關係卻跟題目例子是有相關性的時候，就可以當作 support 的答案選項:
For example:
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Although exposure to asbestos is the primary cause of mesothelioma, a slow-developing
cancer, researchers believe that infection by the SV40 virus is a contributing cause, since in
the United States 60 percent of tissue samples from mesotheliomas, but none from healthy
tissue, contain SV40. SV40 is a monkey virus; however, in 1960 some polio vaccine was
contaminated with the virus. Researchers hypothesize that this vaccine was the source of the
virus found in mesotheliomas decades later.
Which of the following, if true, most strongly supports the researchers' hypothesis?
(A) SV40 is widely used as a research tool in cancer laboratories.
(B) Changes in the technique of manufacturing the vaccine now prevent contamination with SV40.
(C) Recently discovered samples of the vaccine dating from 1960 still show traced of the virus.
(D) In a small percentage of cases of mesothelioma, there is no history of exposure to asbestos.
(E) In Finland, where the polio vaccine was never contaminated, samples from mesotheliomas do not contain SV40.
Ans: E
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題目是說，在美國發現 SV 40 是 mesothelioma 形成的加速原因。而 1960 polio 疫苗感染了 SV40，所以此疫苗為十年後 mesothelioma 中的 SV40 的來源。
答案選項是，在芬蘭，在 polio 疫苗沒有感染的地方， mesothelioma 並沒有 SV 40。這個答案的平行，完全符合第一類型的完全相反因果。
但有許多同學不選此答案的原因，是因為芬蘭並沒有出現在題目當中。但在 GMAT 題目當中，除非題目有強調地區性的概念 (譬如政策，方案)，不然如果是相同的因果關係，便可拿來當作 support 的答案選項。此題雖然有講到美國，但講到結論句時，並沒有強調地區性的特徵了。
雖然這裡是講 support，但在此拿一題 Weaken 的題目來討論:
For example:
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An unusually severe winter occurred in Europe after the continent was blanketed by a blue
haze resulting from the eruption of the Laki Volcano in the European republic of Iceland in
the summer of 1984. Thus, it is evident that major eruptions cause the atmosphere to become
cooler than it would be otherwise.
Which of the following statements, if true, most seriously weakens the argument above?
(A) The cooling effect triggered by volcanic eruptions in 1985 was counteracted by an unusual warming of Pacific waters.
(B) There is a strong statistical link between volcanic eruptions and the severity of the rainy season in India.
(C) A few months after El Chichn's large eruption in April 1982, air temperatures throughout the region remained higher than expected, given the long-term weather trends.
(D) The climatic effects of major volcanic eruptions can temporarily mask the general warming trend resulting from an excess of carbon dioxide in the atmosphere.
(E) Three months after an early springtime eruption in South America during the late 19th century, sea surface temperatures near the coast began to fall.
Ans: C
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題目是說，在 Laki Volcano 之後出現了寒冬。所以大規模的火山爆發就會讓大氣層變寒冷。
五個答案選項，沒有任何答案出現 Laki Volcano。而正確答案選項: El Chichn's eruption 產生了長期高溫的趨勢。
看似不同的例子，但卻不是無關，因為題目的結論並沒有特別強調地區性，所以相似概念的因果關係，就可拿來做 weaken 的答案選項 (當然，另外四個答案選項完全是 support 方向，或是無關的答案)。
所以在結論沒強調特殊地點和概念時，我們可以以相同觀念的例子，來 support or weaken。
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