The Contractual Rule That Requires an Exchange of Value

The contractual rule that requires an exchange of value

A) is based on the need for clear evidence of an agreement and therefore does not apply if the parties' agreement is written, rather than oral.
B) cannot be satisfied by the provision of love and affection because that rule requires each party to provide a physical benefit, rather than services or actions.
C) can be satisfied by the use of a seal because a seal is itself a form of valuable consideration.
D) generally requires proof that each party provided sufficient consideration, but it does not also require proof that each party provided adequate consideration.
E) is best explained through the doctrine of privity.