Answer:
The reciprocity norm.
Explanation:
The norm of reciprocity requires that we repay in kind what another has done for or to us. "An eye for an eye" could be described by this norm. In this case, Jacob and Ethan split the rent and the work between themselves. One cooks, the other cleans. The reciprocity norm requires to pay in kind, be it positive or negative.
A good sentence for a social contract is that a social contract is an abstract term which denotes how a specific society is organized and what are the relations between people who live within this society and which characterize them as members of the society but also as smaller groups within it.
I think the answer might be A