[Refusal to Pay] Business Law Teacher Allison Needed Some Yard

[Refusal to Pay] Business law teacher Allison needed some yard work done. She told her class that she would give $50 to the first person who mowed her yard. She also entered into an agreement with Karina who agreed to trim some shrubbery for $40. Another student, Brendan, went to mow Allison's yard. Unfortunately, just as he finished mowing, a neighborhood dog bit him, and he had to go to the emergency room for a couple of stitches. Allison refused to pay Brendan because she said that he had upset the neighbors and their dog, and that he was more trouble than he was worth. Secretly, Allison was glad about the dog bite because she felt it gave her a reason not to pay. Brendan refused to pay the emergency room because he said that they did not have a binding, bilateral contract. Karina refused to trim the shrubbery because she got a better offer and claimed that she was not bound on the contract until she started the work.
-Which of the following is correct regarding Karina's statement that there was no contract?

A) Karina is correct. There was no contract because she had not started working.
B) Karina is incorrect because there was a bilateral, express agreement.
C) Karina is incorrect because there was a bilateral, implied agreement.
D) Karina is incorrect because there was a unilateral, express agreement.
E) Karina is incorrect because there was a unilateral, implied agreement.