Mandy offers to pay David $$1,000$ for David's computer, provided that Mandy receives that much from her aunt's estate, which is currently being probated. She expects to know for sure how much she will receive within a week or so$.$ In this case:

Select one:

a$.$ this is an illusory contract, because Mandy doesn't know whether she will receive the money for sure.

b$.$ Mandy's conditional promise is sufficient consideration unless Mandy knows she cannot receive at least $$1,000$ from her aunt's estate.

c$.$ There is no consideration.

d$.$ the consideration of the promise of $$1,000$ is insufficient because it is subject to a condition.