求教一道rc考古

nyonko

Mostfarmers attempting to control slugs and snails turn to baited slug poison, ormolluscicide, which usually consists of a bran pellet containing eithermethiocarb or metaldehyde.  Bothchemicals are neurotoxins that disrupt that part of the brain charged withmaking the mouth move in a coordinated fashion--the "central patterngenerator"--as the slug feeds. Thus, both neurotoxins, while somewhat effective, interfere with theslugs' feeding behavior and limit their ingestion of the poison, increasing theprobability that some will stop feeding before receiving a lethal dose.  Moreover, slugs are not the only consumers ofthese poisons:  methiocarb may be toxicto a variety of species, including varieties of worms, carabid beetles, andfish.

Researchers are experimenting with an alternativecompound based on aluminum, which may solve these problems, but this may wellhave a limited future as we learn more about the hazards of aluminum in theenvironment.  For example, someresearchers suggest that acid rain kills trees by mobilizing aluminum in thesoil, while others have noted that the human disease Alzheimer's is moreprevalent in areas where levels of aluminum in the soil are high.  With farmers losing as much as 20 percent oftheir crops to slugs and snails even after treatment with currently availablemolluscicides, there is considerable incentive for researchers to come up withbetter and environmentally safer solutions.----------------------
The passage suggests that methiocarband metaldehyde would be more effective as slug poisons if it were true thatthey


(A)disrupt the slug's digestive processes rather than its reproductive functions
(B)reduce the slug's ability to taste food
(C)begin to affect the feeding behavior of a slug only after it has ingested alethal dose
(D)reach the central pattern generator more quickly
(E)accumulate only in the central pattern generator rather than throughout thebrain


答案是C，但我看到文中只提到目前两m作用原理是不足lethal dose时就影响feed behavior
有大侠能帮忙解释下为什么选C吗？谢谢谢谢！！！！！！！！！！