SAT Writing SAT is tomorrow... Please Help!

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1
  1. The research study reveals startling proof of a constant changing seafloor that comprises the major part of the underwater landscape. - I understood that "constant" should be changed to "constantly", but I also thought "part" should be changed to "parts" since it says comprise (which means combining multiple objects).

Thanks in advance.

2

comprises = makes up
in this sentence.

3

Comprise usually takes a plural object, but it is not a rule. You can say things like “The United States comprises roughly 40% of North America.”

4

Thank you! To construe comprise as “makes up” really helps me understand this sentence.