How Can the Concept of Unforeseen Difficulties Affect Whether a Contract

How can the concept of unforeseen difficulties affect whether a contract meets the consideration requirements?

A) Unforeseen difficulties can allow a promise of illegal consideration to meet the consideration requirements.
B) Unforeseen difficulties can convert an illusory promise to a valid binding promise.
C) Unforeseen difficulties can result in past consideration meeting the consideration requirements.
D) Unforeseen difficulties can result in a contractor's promise to complete an existing contract being supported by new consideration rather than being considered a preexisting duty.
E) Unforeseen difficulties cannot affect whether a contract meets consideration requirements.