考生在考試中經常會遇到這樣一種現象，在題幹中遇到了一個teenager，但是在文章中找對應信息的時候，出現的卻是young people;題幹中遇到的是punctually，文中對應的是on time。這個就是PET考試中一個常見的考點，同義替換。
同義替換，簡單來說，有時可以是名詞替換名詞，動詞替換動詞。這種情況比較簡單。但是有時候，還會出現另外一種情況，例如題幹中是 on busy school roads, 文章當中是heavy traffic in towns and cities。你會發現它的結構整個是不一樣的，一個是介詞短語，一個是名詞性結構，這種同義替換相對來說難度更大一些。
對於考生來說，主要的一個難點就是單詞基本認識，就是選不對答案。因此想要掌握同義替換，需要進行大量的練習。
在PET閱讀中，同義替換有四種典型的方式：
1.同義詞之間的替換
題目：Feeding increasing populations is possible due primarily to improved irrigation systems.
原文：Food production has kept face with soaring population mainly because of the expansion of artificial irrigation system that make possible the growth of 40% of the world’s food.
分析：此題出現的同義詞替換包括：
feeding → food production
due primarily to→mainly because of
improved irrigation systems→the expansion of artificial irrigation system.
典型的同義詞替換：
change →shift / revision
metropolitan →city
overstate →exaggerate
expert →scientist / specialists
target →goal
decrease→crash / halve
comments →feedback
hard to find →elusive
like → resemble
2.同根詞詞性的替換
題目：They use their own natural secret antibiotics as weed-killers and also use unwanted materials as fertilizers.
原文：Farmer ants secrete antibiotics to control other fungi that might act as 』weeds』, and spread waste to fertilize the crop.
分析：此題中出現的同根詞詞性替換包括：
secrete antibiotics → secretion
fertilizer →fertilize.
3.否定加反義詞之間的替換
題目：In principle, it is possible for a biological system to become older without ageing.
原文：Thus ageing and death should not be seen as inevitable, particularly as the organism possesses many mechanism for repair.
分析：題幹中possible是原文not inevitable的否定加反義替換。
典型的否定加反義詞替換：
downward →not rising
not traditional →radical new approaches
with no rain at all →droughts
4.上下義詞的替換
所謂上下義，是指替換的詞語之間通常有一種從屬關係。題目中給的是一個具有屬性或者是表示概念的詞語，而在原文中出現的替換詞卻是一個具體或者是細節的信息，此類替換考察的是考生對這兩者之間從屬關係的配對。
題目：Studies show drugs available today can delay the process of growing old.
原文：As researchers on aging noted recently, no treatment on the market today has been proved to slow human aging—the build-up of molecular and cellular damage that increases vulnerability to infirmity as we get older.
分 析：原文中treatment即為題幹中drugs的上義詞。
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