At the time a buyer was negotiating the purchase of a lot on which to build a new home, the seller represented that the soil was firm enough to support the construction of a
building when, in fact, the seller knew it was not. This contract is

a. voidable by neither party because no harm was done yet.
b. void.
c. voidable by the seller because of the mistake.
d. voidable by the buyer because of fraud.