请教各位，该题E为何不是正确答案？

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.