OG上將推斷題定義為檢查考生對文章中強烈建議但絕不明說觀點(strongly implied but not explicitly stated in the text)的理解程度，屬於理解性題目，題目要求如下：
Which of the following can be inferred from paragraph 2 about X?
According to paragraph 5, what does the author imply about X ?
Paragraph 1 suggests which of the following about X?
According to paragraph 3, what do Y indicate about X?
題幹中有出現infer, imply, indicate或suggest這四個單詞，我們就判定一個題目為推斷題，那推斷題如何解答呢?
前三步，可以借用做事實資訊題的方法來做，最後一步的推測，相對于正向推理，逆向推理對同學們簡單一些，回到原文中定位，發現相關句中存在著對比或轉折的，直接否定前者，得出答案，例如TPO2中的The Origins of Cetaceans 的第2題，讓你推測關於early sea otters的，回到原文中定位，你會發現，關鍵句中存在著一個unlike，說不像sea otters，想像一下早期鯨類比較困難(not easy=difficult)，那我們逆推一下，不就是說想像早期sea otters長什麼樣比較容易，正確答案中出現了not difficult，所以這道題很簡單，當然ETS不會一直都出這麼簡單的推斷題，只是給大家一個答題的方向，另外，ETS經常會在有時間對比處出推斷題，這時候我們逆向推理就可以得出正確答案，下面看一個例題：
3. Which of the following can be inferred from paragraph 2 about canal building?
○ Canals were built primarily in the south of England rather than in other regions.
○ Canal building decreased after the steam locomotive was invented.
○ Canal building made it difficult to study rock strata which often became damaged in the process.
○ Canal builders hired surveyors like Smith to examine exposed rock strata.
Paragraph 2: This was before the steam locomotive, and canal building was at its height. The companies building the canals to transport coal needed surveyors to help them find the coal deposits worth mining as well as to determine the best courses for the canals. This job gave Smith an opportunity to study the fresh rock outcrops created by the newly dug canal. He later worked on similar jobs across the length and breadth of England, all the while studying the newly revealed strata and collecting all the fossils he could find. Smith used mail coaches to travel as much as 10,000 miles per year. In 1815 he published the first modern geological map, "A Map of the Strata of England and Wales with a Part of Scotland," a map so meticulously researched that it can still be used today.
解析：第一步，我們看到infer判斷為推斷題。第二步，審題得到的資訊點是第2段和canal building。第三步，回到原文定位，相關句為第一句，This was before the steam locomotive, and canal building was at its height.出現了before steam locomotive，有時間對比，canal building was at its height , at one's height處於頂峰。那第四步我們就可以逆向推理到after steam locomotive，canal building 下滑，判定四個選項中只有B符合我們的推測，所以正確選項為B，而ACD都是迷惑你的無關選項。
逆推比較好理解，而正推同學們覺得難的原因是不好把握度，很容易加上自己的主觀判斷就推過了，這時候我們可以把它當做事實資訊題去做，因為你要基於原文進行推測，那麼討論的角度和情感色彩要與原文的保持一致，所以做題的另外一條原則是don't contradict with the main idea of the passage，推測的時候我們可以用演繹或者歸納的方法得出正確答案，也可以借用文章主旨和情感態度選出正確答案，看如下例題：
10. According to paragraph 4, what do the 2003 Global Surveyor data suggest about Mars?
○Ancient oceans on Mars contained only small amounts of carbon.
○The climate of Mars may not have been suitable for the formation of large bodies of water.
○Liquid water may have existed on some parts of Mars' surface for long periods of time.
○The ancient oceans that formed on Mars dried up during periods of cold, dry weather.
Paragraph 4: These ideas remain controversial. Proponents point to features such as the terraced "beaches" shown in one image, which could conceivably have been left behind as a lake or ocean evaporated and the shoreline receded. But detractors maintain that the terraces could also have been created by geological activity, perhaps related to the geologic forces that depressed the Northern Hemisphere far below the level of the south, in which case they have nothing whatever to do with Martian water. Furthermore, Mars Global Surveyor data released in 2003 seem to indicate that the Martian surface contains too few carbonate rock layers-layers containing compounds of carbon and oxygen-that should have been formed in abundance in an ancient ocean. Their absence supports the picture of a cold, dry Mars that never experienced the extended mild period required to form lakes and oceans. However, more recent data imply that at least some parts of the planet did in fact experience long periods in the past during which liquid water existed on the surface.
解析：根據關鍵字我們定位到文段的中間部分：Mars Global Surveyor data released in 2003 seem to indicate that the Martian surface contains too few carbonate rock layers-layers containing compounds of carbon and oxygen-that should have been formed in abundance in an ancient ocean.這道題可以當做事實資訊題去做，但注意不是原文的簡單重複，suggest 是原文中indicate的同義轉換，我們只要找到what就好了，原文that後面是重點，出現了too few, should have, 情感態度推測一下，持否定態度，也就說說形成 an ancient ocean不太可能，我們看選項，A中說Ancient oceans on Mars contained only small amounts of carbon.主客體與原文矛盾，排除;B選項 The climate of Mars may not have been suitable for the formation of large bodies of water.說不適合形成大量的水，持否定態度，符合原文，保留;C選項Liquid water may have existed on some parts of Mars' surface for long periods of time.相關句中未提及，排除;D選項The ancient oceans that formed on Mars dried up during periods of cold, dry weather. 說的是ancient oceans沒有，而不是原來有後來乾涸了，與原文不符，排除，所以正確答案為B。