Jahna and Ike Contract for the Sale of Jahna's Horse

Multiple Choice

Jahna and Ike contract for the sale of Jahna's horse for $1,000. Unknown to either party, the horse has died. Ike is

A) entitled to another horse of equivalent value.
B) not required to pay due to the mutual mistake.
C) not required to pay due to the unilateral mistake.
D) required to pay because he assumed the risk the horse might die.