Bailey Agrees to Bathe and Groom Keiko's Dog,Fluffy,for $30

Bailey agrees to bathe and groom Keiko's dog,Fluffy,for $30.Bailey agreed to the price prior to seeing Fluffy,who is a large dog with lots of hair.Bailey tells Keiko that if she is going to groom Fluffy,the price will be $40.Keiko reluctantly agrees but tells Bailey that she should not have been surprised that a dog named Fluffy would have lots of hair.Bailey bathes and grooms Fluffy,but Keiko only pays her $30.Which of the following is correct regarding Bailey's entitlement to the extra $10?

A) Assuming the unforeseen circumstances rule does not apply,Bailey is not entitled to the extra $10 because she had a preexisting duty to bathe and groom Fluffy for $30.
B) Assuming the unforeseen circumstances rule does not apply,Bailey is not entitled to the extra $10 because past consideration was involved.
C) Bailey is entitled to the extra $10 because a valid bilateral contract existed.
D) Bailey is entitled to the extra $10 because a valid unilateral contract existed.
E) Assuming the unforeseen circumstances rule does not apply,Bailey is not entitled to the extra $10 because Keiko's promise to pay $30 was illusory.