“六选三”的主旨题是托福阅读最后一道大题最常出现的题型之一，即从六个选项中选取三个，加上给出的句子，合成对全文主要观点的概括。正确选项的特征是"the most important ideas in the passage"，是文章的核心信息;反过来说，错误选项除了可能是文章根本没有涉及的信息之外，典型特征之一是过多关注文章细节而不是主要观点。下面我们以两个题目分别来看如何判断主旨信息和细节信息。
例题1：MINERALS AND PLANTS
Paragraph 1 Research has shown that certain minerals are required by plants for normal growth and development.
Paragraph 2 Mineral deficiencies can often be detected by specific symptoms such as chlorosis (loss of chlorophyll resulting in yellow or white leaf issue), necrosis (isolated dead patches), anthocyanin formation (development of deep red pigmentation of leaves or stem), stunted growth, and development of woody tissue in an herbaceous plant.
Paragraph 3 Much of the research on nutrient deficiencies is based on growing plants hydroponically, that is, in soilless liquid nutrient solutions.
Paragraph 4 While mineral deficiencies can limit the growth of plants, an overabundance of certain minerals can be toxic and can also limit growth.
Paragraph 5 Scientists have known for some time that certain plants, called hyper accumulators, can concentrate minerals at levels a hundredfold or greater than normal.
Paragraph 6 Only recently have investigators considered using these plants to clean up soil and waste sites that have been contaminated by toxic levels of heavy metals - an environmentally friendly approach known as phytoremediation.
Directions: An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage. Some answer choices do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points.
Plants need to absorb certain minerals from the soil in adequate quantities for normal growth and development.
1. Some plants are able to accumulate extremely high levels of certain minerals and thus can be used to clean up soils contaminated with toxic levels of these minerals.
2. Though beneficial with lower levels, high levels of salts, other minerals, and heavy metals can be harmful to plants.
3. When plants do not absorb sufficient amounts of essential minerals, characteristic abnormalities result.
4. Because high concentrations of sodium chloride and other salts limit growth in most plants, much research has been done in an effort to develop salt-tolerant agricultural crops.
5. Some plants can tolerate comparatively low levels of certain minerals, but such plants are of little use for recycling nutrients back into depleted soils.
6. Mineral deficiencies in many plants can be cured by misting their roots with a nutrient solution or by transferring the plants to a soilless nutrient solution.
例题2：APPLIED ARTS AND FINE ARTS
An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage. Some sentences do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points.
This passage discusses fundamental differences between applied-art objects and fine-art objects.
○Applied-art objects fulfill functions, such as containing or sheltering, and objects with the same function have similar characteristics because they are constrained by their purpose.
○It is easy to recognize that Shang Dynasty vases are different from Inca vases.
○Fine-art objects are not functional, so they are limited only by the properties of the materials used.
○Renaissance sculptors learned to use iron braces to strengthen the internal structures of bronze statues.
○In the twentieth century, fine artists and applied artists became more similar to one another in their attitudes toward their materials.
○In all periods, fine artists tend to challenge the physical limitations of their materials while applied artists tend to cooperate with the physical properties of their materials.
错误选项为245.它们共同的特点是：细节信息，具体体现在：选项2里的Shang Dynasty vases, 选项4的Renaissance sculptors, 选项5里的in the twentieth century和similar。这些细节信息的具体特征是：人名、地名、数字、年代等等。尤其当这些信息出现在句子主干处时，要格外当心!