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Sentence Correction: Subject Verb Agreement - X of Y Subject

Compensating for the lack of oxygen in a high altitude atmosphere, Tibetans produce boosted supplies of nitric oxide in their bloodstream; this chemical compound, according to researchers, allows blood vessels to expand and increase the blood flow.

Incorrect.

This answer choice is illogical.

This sentence begins with a modifier: Compensating for the lack of oxygen in a high altitude atmosphere. A modifier should be placed right next to the noun it describes. The only noun that this modifier can logically modify is Tibetans. The noun Tibetans, however, is quite far from the modifier that describes it. Therefore, it seems as though researchers are compensating for the lack of oxygen, and not the Tibetans.

[[snippet]]

Incorrect.

This answer choice is stylistically flawed. The phrase are the producers of boosted supplies is awkward and creates Redundancy. Look for a more concise answer choice.

Incorrect.

This answer choice is illogical.

This sentence begins with a modifier: Compensating for the lack of oxygen in a high altitude atmosphere. A modifier should be placed right next to the noun it describes. The only noun that this modifier can logically modify is Tibetans. The noun Tibetans, however, is quite far from the modifier that describes it. Therefore, it seems as though researchers are compensating for the lack of oxygen, and not the Tibetans.

[[snippet]]

In addition, in the corrected sentence, the plural verb is matched to the plural subject boosted supplies. However, logically speaking, it is not the supplies that cause blood vessels to expand, but nitric oxide.

Incorrect. While this answer choice may seem more concise because the relative clause _which...allows blood vessel to expand, etc._ is now turned into a **V+ing modifier** the meaning is unclear because of the final phrase _according to researchers_. It is not possible to know what this phrase modifies in the previous clause exactly. In the **original sentence** it is clear that researchers make a connection between the _chemical compound_ and the expanding and increasing of the blood flow.

Impressive work!

A modifier should be placed right next to the noun it describes. In this answer choice, the noun Tibetans directly follows the modifier Compensating for the lack of oxygen in a high altitude atmosphere, indicating that the Tibetans are the ones who compensate for the lack of oxygen, rather than the researchers (in answer choices C and E.

Tibetans produce boosted supplies of nitric oxide in their bloodstream; this chemical compound, according to researchers, allows blood vessels to expand and increase the blood flow
Tibetans produce boosted supplies of nitric oxide in their bloodstream, allowing blood vessels to expand and increase the blood flow, according to researchers
researchers found that Tibetans produce in their bloodstream boosted supplies of nitric oxide, which cause blood vessels to expand and increase the blood flow
Tibetans are the producers of boosted supplies of nitric oxide; this chemical compound allows blood vessels to expand and increase the blood flow, according to researchers
researchers have found that Tibetans produce boosted supplies of nitric oxide in their bloodstream, causing blood vessels to expand and increasing the blood flow