Jake dove into a surging stream to save Sandra$$s purebred, $$25,000$ sheepdog from drowning. In gratitude, Sandra agreed to buy Jake a pizza on the last day of each of the next twelve months. Although a nice gesture, Sandra is really not bound to buy the pizza because of the doctrine of:

Group of answer choices

a$.$ Nominal consideration

b$.$ Moral consideration

c$.$ Pre$-$existing duty

d$.$ Past consideration

e$.$ B and D above