Essay #11.316
Most farmers attempting to control slugs and snails turn to baited slug poison, or molluscicide, which usually consists of a bran pellet containing either methiocarb or metaldehyde.Both chemicals are neurotoxins that disrupt that part of the brain charged with making the mouth move in a coordinated fashion--the "central pattern generator"--as the slug feeds.Thus, both neurotoxins, while somewhat effective, interfere with the slugs' feeding behavior and limit their ingestion of the poison, increasing the probability that some will stop feeding before receiving a lethal dose.Moreover, slugs are not the only consumers of these poisons:methiocarb may be toxic to a variety of species, including varieties of worms, carabid beetles, and fish.
Researchers are experimenting with an alternative compound based on aluminum, which may solve these problems, but this may well have a limited future as we learn more about the hazards of aluminum in the environment.For example, some researchers suggest that acid rain kills trees by mobilizing aluminum in the soil, while others have noted that the human disease Alzheimer's is more prevalent in areas where levels of aluminum in the soil are high.With farmers losing as much as 20 percent of their crops to slugs and snails even after treatment with currently available molluscicides, there is considerable incentive for researchers to come up with better and environmentally safer solutions.
Question #36.316-01
In the passage, the author is primarily concerned with
(A) describing the limitations of molluscicides that affect feeding behavior
(B) proposing alternatives to current methods of controlling slugs and snails
(C) emphasizing the need for an alternative to currently available molluscicides
(D) explaining how molluscicides are used to control slugs and snails
(E) criticizing the use of hazardous material for controlling slugs and snails
这题答案选C，请问怎么是强调两种方法替换的需要呢？为什么不是
E呢？
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