Final answer:
Legal consideration is something of value that is exchanged between parties in a contract, and b. A promise based upon a change in duties and payments qualifies as such. Consideration must involve a new bargain or exchange of value to be enforceable; moral obligations alone do not suffice for legal consideration.
Step-by-step explanation:
Legal consideration refers to something of value exchanged between parties in a contract. The correct answer to which of these constitutes legal consideration is b. A promise based upon a change in duties and payments. This choice involves a mutual exchange that is legally enforceable. A promise to make a gift (a) is usually not enforceable because it lacks the exchange element, a promise based on moral obligation (c) is not enough to constitute legal consideration as it does not have a tangible legal benefit or detriment, and promises based on past consideration (d) or a preexisting duty (e) also typically do not qualify as consideration because they do not involve a new bargain or exchange.
In the context of Ross's prima facie duties, while a promise to meet a friend can represent a duty of fidelity, intervening to help a coworker in distress may invoke the duty of non-maleficence or a duty of reparation should the coworker have been harmed. However, these moral obligations do not translate directly into legal consideration.
Responsibilities like serving as a juror or in the Armed Forces could be legal or moral. Serving as a juror is a legal duty required under the law, whereas serving in the Armed Forces may be seen by some as a moral duty, though it can also be legally mandated in some jurisdictions through conscription.