12. Mercury, one of the deadliest toxins, makes up approximately fifty percent of the amalgam used by dentists in sliver fillings. The effects of acute mercury poisoning are known-kidney failure, muscle tremors, memory loss, and even death. It is clear that responsible dentists should remove all of the patients silver fillings and replace then with filling of plastic composites.
Which of the following, if true, most strengthens the author's argument?
(A) Sliver fillings gradually corrode and small amounts of mercury leak from the amalgam.
(B) It is difficult to measure the amount of mercury in a person's body.
(C) Some patients have more than one filling per tooth.
(D) Mercury poisoning produces a range of subtle but distinctive symptoms.
(E) The materials for plastic composite fillings are readily available to dentists.

答案是A，据网络课堂里狒狒的说法是：加强结论，就去掉水银就可以了，但我就不太明白为什么只须加强去掉水银的必要性，而不需要考虑结论中所说的“用塑料来替代”？我选的E，因为我想原文中已经明确指出水银毒害性很大，结论是要去掉水银而换成塑料，塑料是原来前提中没有的信息，但结论中却突然出现，那么应该需要一句话来说明一下，才能加强结论。

不知道我的逻辑错在哪里，请大家指教！

个人以为完整的推理思路应为mercury有毒----〉人会接触到mercury------〉mercury对人有害；但题干缺少中间环节，即，虽然mercury有毒，但只要完全封在了silver filling里，对人也是无害的；对此进行弥补即为加强。

因此，本题为假设型加强考题，读出GAP并加以弥补为考点。

仅供参考。

哦，刚刚想起来狒狒说过离结论标志词最近的结论是最重要的结论，我想是不是这题就表明结论中and的前半句是主要结论后半句是次要结论，所以加强的话，加强前半句更重要。

另外，什么叫GAP？不太明白.

 GAP=gap,就是逻辑断层。

我个人觉得您想的太多了~~~