Answer:
D) enforce the contract.
Step-by-step explanation:
Neither party knew about the gold mine before the deal was made, Byron and Charity even thought it was worthless. If Charity by accident, chance or luck discovered the gold mine, then she is entitled to it. Even f Byron wants to cancel the deal, he can't because Charity acted on good faith and the discovery of the gold mine was not something planned or intended.
For example, if I like an antique at a yard sale and I purchase it at $5, and then by chance someone that knows about antiques tells me that it is really expensive, a made a lot of money and the previous owner doesn't have the right to cancel the sale.