Which type of contract is based solely on the conduct of the involved parties?

The correct answer is based on the definition of an implied contract. An implied contract is established by the actions or conduct of the parties involved rather than through explicit written or spoken agreements. This type of contract arises when the circumstances imply that the parties have agreed to certain terms, even if they have not formally articulated those terms.

For instance, if someone goes to a restaurant, orders food, and eats a meal, there is an implied contract that they will pay for the meal, even though no formal agreement was signed. The conduct of ordering and consuming the food indicates that there is an understanding that payment is expected.

In contrast, a bilateral contract involves a clear agreement where both parties make promises to each other, often articulated in a formal manner. An express contract also entails a clear agreement, but it is explicitly stated, either in written or verbal form. A unilateral contract arises when one party makes a promise in exchange for an act by another party, which does not rely solely on conduct but rather on a specific promise followed by an action.

Thus, the nature of how implied contracts are formed through conduct distinctly sets them apart from these other types of contracts.