Paragraph5: Scientists have known for some time that certain plants, called hyper accumulators, can concentrate minerals at levels a hundredfold or greater than normal. A survey of known hyper accumulators identified that 75 percent of them amassed nickel, cobalt, copper, zinc, manganese, lead, and cadmium are other minerals of choice. Hyper accumulators run the entire range of the plant world. They may be herbs, shrubs, or trees. Many members of the mustard family, spurge family, legume family, and grass family are top hyper accumulators. Many are found in tropical and subtropical areas of the world, where accumulation of high concentrations of metals may afford some protection against plant-eating insects and microbial pathogens.
Why does the author mention herbs, shrubs, and trees?
¡ To provide examples of plant types that cannot tolerate high levels of harmful minerals.
¡ To show why so many plants are hyper accumulators.
¡ To help explain why hyper accumulators can be found in so many different places.
¡ To emphasize that hyper accumulators occur in a wide range of plant types.
题中问为何提到这三种植物，正常的思维是作者为了说明前面的概述，因此往前看一句即可：Hyper accumulators run the entire range of the plant world。意思为富集植物广泛分布于整个植物界。不难得出答案为第四个. 这是修辞目的题最基本的解题方法，我们称之为“绕过例子看概述”，如果还有更多托福考试的疑问都可以咨询Marina老师：027-51888555