Which of the following is NOT a characteristic of a bilateral contract?

In a bilateral contract, both parties agree to perform certain obligations. This means that each party has a duty to act or provide something of value to the other party. Therefore, identifying the characteristic that "only one party must act" as not applicable reflects a correct understanding of bilateral contracts.

In such agreements, unlike unilateral contracts where one party makes a promise in exchange for an act by the other, both parties are required to fulfill their promises. This mutuality of obligation is fundamental to the definition of a bilateral contract.

The other characteristics provided correctly describe bilateral contracts. Both parties indeed have obligations, demonstrating the mutual commitment essential in these types of agreements. Such contracts can be made either in writing or verbally, which provides flexibility in how they are formed. Finally, bilateral contracts are legally enforceable, ensuring that parties can seek recourse if the terms are not met as agreed.