Carlos and david contract for the sale of five hundred head of carlos's cattle for $95 per head. unknown to either party, an unforeseen storm has struck the herd and many of the cattle have died. david is select one:

a. not required to pay due to the bilateral mistake.
b. required to pay because he assumed the risk the cattle might die.
c. not required to pay due to the unilateral mistake.
d. entitled to recover the value of the lost cattle.