Yolanda Agrees to Bathe and Groom Wendy's Dog, Fluffy, for $20

Yolanda agrees to bathe and groom Wendy's dog, Fluffy, for $20. Yolanda agreed to the price before seeing Fluffy, a very plump, grouchy Pembroke Welsh Corgi dog with lots of hair. Yolanda tells Wendy that if she is going to groom Fluffy, the price will be $30. Wendy agrees although noting that the dog is named "Fluffy." Yolanda bathes and grooms Fluffy, but Wendy will only pay $20. Which of the following is correct regarding Yolanda's entitlement to the extra $10?

A) Yolanda is entitled to the extra $10 because a valid bilateral contract existed.
B) Yolanda is entitled to the extra $10 because a valid unilateral contract existed.
C) Assuming the unforeseen circumstances rule is inapplicable, Yolanda is not entitled to the extra $10 because she had a preexisting duty to bathe and groom Fluffy for $20.
D) Assuming the unforeseen circumstances rule is inapplicable, Yolanda is not entitled to the extra $10 because Wendy's promise to pay $30 was illusory.
E) Assuming the unforeseen circumstances rule is inapplicable, Yolanda is not entitled to the extra $10 because past consideration was involved.