来看看几道ＧＲＥ题

２.Although spinach is rich in calcium, it also contains large amounts of oxalic acid, a substance that greatly impedes calcium absorption by the body. Therefore, other calcium-absorption foods must be eaten either instead of or in addition to spinach if a person is to be sure of getting enough calcium.

which of the following, if true, most seriously weakens the argument above?

A.Rice, which does not contain calcium, counteracts the effects of oxalic acid on calcium absorption.

D.Many leafy green vegetables other than spinach that are rich in calcium also contain high concentrations of oxalic acid．

选Ａ

结论是：其它含C食物需要单独吃或者吃了S后补充吃，如果你想得到足够的C。

A说大米可以将S里影响C吸收的效果给消去；也就是说可以将大米与S一块吃

D说有与S效果一样的蔬菜，那按照文中的思路，还是能得出结论，只不过多了几样S一样的东西；不能削弱。

MM再读一下题，看结论和问题分别是什么。