Kim and Mia enter into a a contract for the sale of Kim's collie, Abby, $1,000. Unbeknownst to either Kim or Mia, Abby dies half an hour before the contract is signed. Mia

a.) must be provided another collie or equivalent value by Kim

b.) is still obligated to pay $1,000 to Kim because she assumed the risk that Abby might die at any time

c.) is not required to pay anything due to mutual mistake

d.)is not required to pay anything due to the unilateral mistake