Choose the incorrect statement from the definitions below.

a$.$ A simple contract may be oral or written, but is not under seal.

b$.$ A parol contract is a probationary agreement.

c$.$ A formal contract is one that is sealed by the party to be bound.

d$.$ An implied contract is inferred from the conduct of the parties.

e$.$ An express contract is one in which the parties have expressly stated their agreement, either orally or in writing.