Question

What's the Buzz All About?
by B. McSwain

A West African tale explains that mosquitos buzz in people’s ears because the mosquitos want to know if people are still angry about the calamity a mosquito once caused in the jungle. Researchers, however, have found a scientific explanation for this bane on the human ear. Mosquitos buzz because they fly, beating their wings up to 800 times per second to create their annoying sound. Only females need blood for the eggs they produce. Therefore, only a female will be stabbing flesh with her long proboscis, and to find this life-giving flesh, the mosquito searches for moisture, body heat, and carbon dioxide. Females have unique receptors in their nerve cells that detect carbon dioxide and human skin odor. Researchers have found this receptor can be shut down after brief exposure to certain chemicals. But even if the carbon dioxide detector is shut down, the mosquito will still be able to detect skin odor, so holding one's breath will be ineffective as a mosquito deterrent.
Finding a compound that is effective, pleasant to smell, inexpensive, and safe for humans has been as woeful for researchers as the buzzing itself. Using a computer, researchers screened almost a half a million chemical compounds to find ones that would interact with the mosquito's receptor. This enabled them to sift the compound pool down to a manageable number of compounds—just over 100. From there, two compounds have proved very promising. One compound attracts mosquitos even better than carbon dioxide and could be used to lure the pests into traps. Another compound, called ethyl pyruvate, actually masks human odor and blocks mosquitos from being attracted to the flesh. Both compounds are considered safe for human use and could be used together to offer relief from these insects. This could bring much needed relief in regions where mosquito-borne diseases are widespread.

1
Which evidence from the passage best supports the idea that finding a safe and effective compound has been a challenging experience for researchers?
A.
two compounds have proved very promising
B.
could be used to lure the pests into traps
C.
researchers screened almost a half a million chemical compounds
D.
enabled them to sift the compound pool down to a manageable number
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Answer 1

The evidence from the passage that best supports the idea that finding a safe and effective compound has been a challenging experience for researchers is:

C. researchers screened almost a half a million chemical compounds.

This indicates the extensive effort and the large number of compounds they had to evaluate, suggesting the difficulty of the task.