Question

One summer, floods covered low-lying garlic fields situated in a region with a large mosquito population. Since mosquitoes lay their eggs in standing water, flooded fields would normally attract mosquitoes, yet no mosquitoes were found in the fields. Diallyl sulfide, a major component of garlic, is known to repel several species of insects, including mosquitoes, so it is likely that diallyl sulfide from the garlic repelled the mosquitoes.

Which of the following, if true, most strengthens the argument?
(A) Diallyl sulfide is also found in onions but at concentrations lower than in garlic.
(B) The mosquito population of the region as a whole was significantly smaller during the year in which the flooding took place than it had been in previous years.
(C) By the end of the summer, most of the garlic plants in the flooded fields had been killed by waterborne fungi.
(D) Many insect species not repelled by diallyl sulfide were found in the flooded garlic fields throughout the summer.
(E) Mosquitoes are known to be susceptible to toxins in plants other than garlic, such as marigolds.

Answer 1

(D) Many insect species not repelled by diallyl sulfide were found in the flooded garlic fields throughout the summer.

Step-by-step explanation:

Mosquitoes were not found in the ideal breeding environment provided by the standing water in flooded fields. The fields were planted with garlic plants which are rich in diallyl sulfide and it is known to repel mosquitoes. Hence, mosquitoes were not able to propagate in the garlic fields.

A statement that can strengthen this argument is that insect species which are not repelled by diallyl sulfide were found in the flooded waters. If these insects were also not present then it could have been said that some other factor apart from diallyl sulfide was operating to halt their breeding. Other insect species were probably still present in fields because they are not repelled by diallyl sulfide.