Marco promises to pay his personal chef Davida $$60,000$ in consideration of the services she provided over the years but Marco never makes the payment. Marco's promise is

a$.$

$$not enforceable because the consideration is in the past.

b$.$

$$enforceable to the extent of what Davida$$s services were actually worth.

c$.$

$$enforceable for the entire $$60,000.$

d$.$

$$not enforceable because the failure to pay is an unforeseen difficulty