The following sentence has been split into four segments. Identify the segment that contains a grammatical error.

Several studies support the idea / that the amount of consistent sleep / you receive significantly impacts / a quantity of gray matter in your brain.

The segment that contains a grammatical error is Option A.

The correct phrase should be “the quantity of gray matter in your brain”. So, the corrected sentence would be:

“Several studies support the idea that the amount of consistent sleep you receive significantly impacts the quantity of gray matter in your brain.”

This is because “the” is used before a noun when the specific identity of the noun is known to the reader, whereas “a” is used before a noun when the specific identity of the noun is not known to the reader. In this case, we’re referring to a specific quantity of gray matter (the one in your brain), so “the” is the appropriate article to use.