Jan Promises Eli $4,000 for One of His Original Paintings

Jan promises Eli $4,000 for one of his original paintings on the condition that she receives $1 million from her mother's will. Jan's promise:

A) is illusory.
B) is legally sufficient unless Jan knows she cannot inherit the $1 million.
C) is a conditional promise, which is not sufficient to form consideration.
D) is legally inadequate, and the courts will therefore not enforce it.