1.        GWD-12-Q16:

Certain genetically modified strains of maize produce a natural insecticide that protects against maize-eating insects.  The insecticide occurs throughout the plant, including its pollen.  Maize pollen is dispersed by the wind and often blows onto milkweed plants that grow near maize fields.  Caterpillars of monarch butterflies feed exclusively on milkweed leaves.  When, in experiments, these caterpillars were fed milkweed leaves dusted with pollen from modified maize plants, they died.  Therefore, use of the modified maize inadvertently imperils monarch butterflies.

Which of the following, if true, most seriously weakens the argument?

1. Per unit of volume, the natural insecticide produced by the genetically modified maize plants is less toxic to insects than are many commercial insecticides commonly used on maize plants.

2. Standard weed-control practices that have been used by farmers for decades have largely eliminated milkweed plants from certain areas where monarch-butterfly caterpillars were once common.

3. The experiments showed that the caterpillars were not harmed by contact with the pollen from the genetically modified plants unless they ingested it.

4. The maize-eating insects that the natural insecticide protects against do not feed on the pollen of the maize plant.

5. Airborne maize pollen tends to collect on the middle leaves of milkweed plants and monarch caterpillars feed only on the plant’s tender upper leaves.

谁能解释一下这题的意思

对生物的题一项头大～～～

简单讲~~~

Certain genetically modified strains of maize ＝ A

a natural insecticide ＝B

milkweed plants that grow near maize fields = C

就是A玉米可以产生B杀虫剂，C植物就长在A旁边，风一吹，就把B杀虫剂吹到C植物上面去了。这样子，呆在C上面的蝴蝶的幼虫就吃了染上B杀虫剂的C植物，死了~~~~~

所以说：A玉米对蝴蝶有害！！！

问削弱

E说：Airborne maize pollen tends to collect on the middle leaves of milkweed plants and monarch caterpillars feed only on the plant’s tender upper leaves.

随风而来的B会粘在C植物的中部的叶子上，但是蝴蝶的幼虫只吃C植物最上面的叶子！！

（哈哈，这样子你就伤害不到我了~~~）

题目分析：因：改良的玉米（X）；果：将导致蝴蝶幼虫（Y）死亡（Z）；

weaken方式:原结论是带条件的，必须幼虫吃leaves with pollen，才会 X + Y ——> Z，光有X，Y，但两者没机会结合，就不会导致 Z；

E：正确：我只吃楼上的叶子，你在楼下，我死不了，呵呵；

A：无关，只说了玉米，未将两者建立联系；

B：无关，只说了幼虫生长的植物，但未谈到玉米和幼虫的关系；

C：可能支持原结论，因为幼虫吃了会死；

D：其他虫和本题无关；

；

Airborne maize pollen tends to collect on the middle leaves of milkweed plants and monarch caterpillars feed only on the plant’s tender upper leaves.

By showing that the caterpillar consuming the upper leaves, not the middle leaves, where insecticide pollen collected, they are not risky through such pollination process.