In La Junta,Carlos and Alvaro Contract for the Sale of Five

In La Junta,Carlos and Alvaro contract for the sale of five hundred head of Carlos's cattle for $95 per head.Unknown to either party,a unforeseen storm has struck the herd and many of the cattle have died.Alvaro is​ 

A)  ​entitled to  recover the value of the lost cattle. 
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 cattle might die.