Billy Contracts to Build Harry a House for $100,000

Billy contracts to build Harry a house for $100,000. While laying the foundation, Billy unexpectedly discovers that the area is prone to lightning, to avoid which a lightning rod has to be installed. To ensure that Billy does not delay, Harry agrees to pay $50,000 more than originally agreed. In this unforeseen difficulty arising after the contract is made, in which of the following ways can Billy claim the remaining amount?

A) After the house is constructed, Harry refuses to make the extra payment. The lightning rod costs Billy $100. Harry has no obligation because he only made an illusory promise.
B) After the house is constructed, Harry refuses to make the extra payment. The lightning rod costs Billy $45,000. The problem may be resolved by an accord and satisfaction.
C) After the house is constructed, Harry refuses to make the extra payment. After persistent bargaining, Harry gives a check of $100,100 to Billy, which is encashed by him.
D) After the house is constructed, Harry refuses to make the extra payment. After persistent bargaining, Billy agrees to settle for $90,000 and an old bike from Harry.
E) After the house is constructed, Harry refuses to make the extra payment. After persistent bargaining, Billy agrees to settle for $90,000, if Harry tutored Billy's son.