1. A lack of voluntary consent: a. is one of the four elements of a contract. b. is a defense to the enforcement of a valid contract. c. must be indicated by a clear statement in the contract to which both parties agree.

b. is a defense to the enforcement of a valid contract.

Explanation:

A contract is a written agreement between two individuals, there must be an offer, a consideration, an intention to create legal agreement and a mutual agreement for a contract to be established. Consent is important, it means that both parties in the contract have given due consideration of the terms of the contract and given consent voluntarily. If any of the party attempts to coerce the other party into giving consent, such consent is not voluntary and can be a bases for the annulment of an otherwise valid contract.  

the answer to your question is,

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-mabel < 3