'Elervate' should be 'elevate'. 'Bloodstream' should be plural.
IT because it explains nothing as to what IT IS. That gives us no information and makes no sense
The incorrect word in the sentence is 'elevates', which should be changed to 'elevate' to match the correct grammatical structure. The term 'bloodstream' is correctly used and does not need a plural form. Yawning may help with oxygen intake and brain regulation, but its exact purpose is still being studied.
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