[Textbook Confusion] Jason Needs a Business Law Book

[Textbook Confusion] Jason needs a business law book. He hears that Gwen has one for sale. Jason asks his girlfriend Sakura to buy it for him from Gwen if Sakura can get it for under $40. Sakura sees Gwen in the hall and asks if she will sell the book for $30, and Gwen agrees. They are between classes, and Sakura does not mention that the book is for Jason, although all the parties were on good terms, and the identity of the buyer should not have affected Sakura's agreement. Later, however, Rima agrees to give Jason her used business law book. Jason tells Sakura that he no longer wants the book. Sakura tells Gwen about the situation with Jason. Gwen replies that she does not care if Jason wants the book or not. Gwen says that she passed up a couple of opportunities to sell the book because she thought she already had it sold and that she wants her money from either Gwen or Jason - she doesn't care who pays.
-Which of the following is true regarding whether Jason is liable to Sakura for the cost of the book if Sakura pays Gwen the purchase price?

A) Jason is liable to Sakura for the cost of the book.
B) Jason is liable to Sakura for the cost of the book only if Sakura had Jason sign a document affirming his liability before Sakura paid Gwen.
C) Jason is liable to Sakura only if she resells the book and is unable to recover as much as she paid for it.
D) Jason is not liable to Sakura for the cost of the book.
E) Jason can avoid liability to Sakura only if he can establish that his actions constituted "justifiable expectations" under the law absolving him from liability.