The answer tis'
C) The Mayflower Compact
Tis' C because:
I mean, the question has already explained what the Mayflower Compact is. However, a little interesting observation I've come across may help convince you. (By the way, I could be totally wrong; this is all an observation - I just thought it was interesting and extremely likely to be true.)
So, the ship the settlers of Plymouth (yes, the very same ones from this question) took had a name. What was the name? Why, well the name was Mayflower. Y'know, like the same spelling of Mayflower as the Mayflower Compact.
My assumption is that the Mayflower Compact is named as it is because of its composition. This document's name is a combination of the Mayflower ship, which they came to Plymouth on, and the word Compact: one of which's many definitions is a formal agreement, similar to a treaty or contract.
If you still don't believe me, here's a snippet from an official history textbook with the information you ask for:
