Answer: D. Enforceable because Culler encountered unforeseen difficulties.
Step-by-step explanation:
Contractual obligations can be changed if one or both parties encounter unforeseen circumstances that would significantly alter their ability to fulfil their part of the contract.
In this scenario, Culler Construction would incur a significantly higher cost to carry out their side of the contract than what was agreed. The contract can therefore be changed and this change would be enforceable by law. The higher offer by Orange Key is therefore legal and enforceable.