Final answer:
The elements of an express contract are offer, acceptance, consideration, mutual assent, legality, and capacity, but not duty of care. Duty of care is more relevant to negligence and tort law, making it the correct answer as the element not included in an express contract.
Step-by-step explanation:
The question you've asked relates to the elements of an express contract. Such contracts are legally binding agreements, where the terms are explicitly stated by the parties either orally or in writing. To form an express contract, there must be an offer, acceptance, consideration, mutual assent, and legality. The element of capacity refers to the ability of the parties to enter into a contract, meaning they are of sound mind, not minors, and not under the influence of substances or coercion.
A duty of care does not belong to these foundational elements of an express contract. The duty of care is a concept usually associated with negligence and tort law. It refers to the obligation to avoid causing harm through negligence and is not a necessary component for an express contract to be valid. Therefore, the correct answer to your question is 'd': duty of care.