Final answer:
Kit's attempt to revoke her offer to sell a boat to Liu after Liu has accepted it would be invalid in contract law, as acceptance creates a binding agreement.
Step-by-step explanation:
The question deals with the legal validity of revoking an offer after acceptance in the context of a contract formation. According to the principles of contract law, once an offer is accepted, a binding agreement is formed provided all other elements of contract formation are met.
In this scenario, Kit's attempt to revoke the offer after Liu has accepted would be invalid, because Kit's offer was already accepted by Liu, creating a binding contract. The fact that the contract was not in writing is irrelevant, as a contract does not always need to be in writing to be enforceable. Furthermore, Liu's action of building a dock for the boat can be seen as detrimental reliance, which in some jurisdictions may further prevent Kit from revoking the offer.
Therefore, the correct answer to the question is: b) Invalid, as Liu has already accepted the offer, and a contract is presumably formed.