Yolanda Agrees to Bathe and Groom Wendy's Dog,Fluffy Puff,for $30

Yolanda agrees to bathe and groom Wendy's dog,Fluffy Puff,for $30.Yolanda agreed to the price before seeing Fluffy Puff who is a chubby dog with lots of hair.Yolanda tells Wendy that if she is going to groom Fluffy Puff,the price will be $40.Wendy reluctantly agrees but tells Yolanda that she should not have been surprised that a dog named Fluffy Puff would have lots of hair.Yolanda bathes and grooms Fluffy Puff,but Wendy will only pay $30.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 does not apply, Yolanda is not entitled to the extra $10 because she had a preexisting duty to bathe and groom Fluffy Puff for $30.
D) Assuming the unforeseen circumstances rule does not apply, Yolanda is not entitled to the extra $10 because Wendy's promise to pay $30 was illusory.
E) Assuming the unforeseen circumstances rule does not apply, Yolanda is not entitled to the extra $10 because past consideration was involved.