B is corrent because an executory contract is one that has not been fully performed by both parties. The lessor must provide the building over the term of the lease and the lessee must pay rent.
A is incorrect because a quasi contract is not a real contract; it is a legal obligation created by public policy.
C is incorrect because a unilateral contract is one that involves a promise by one of the parties.
D is incorrect because an implied contract is one in which specific terms must be inferred.
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