Reference - Third-Party Woes

Reference - Third-Party Woes. Trudy owed Sam $40 for a book she purchased from him. Trudy mowed Betty's yard for $40 and agreed with Betty that Betty would pay Sam for the book. Sam is not initially aware of the agreement. Betty pays no one. Trudy also mowed Bob's yard for $40 in return for Bob's agreement to give the payment to Sally representing Trudy's birthday present to Sally. Bob later refuses to do so saying that promises to give gifts are not enforceable. He then moves out of town. Trudy tells both Sam and Sally that she is broke, that Sam needs to get his $40 for the book from Betty, and that Sally is owed $40 from Bob for her birthday present. Which of the following would be the likely result if Sally sues Trudy for the $40 promised to her for her birthday?

A) Sally will win because Trudy is responsible for Bob's failure to pay.
B) Sally will win only if she can prove that Bob is insolvent and unable to pay.
C) Sally will win only if she can prove that she cannot find Bob in order to serve process on him.
D) Sally will win only if she can prove both that Bob is insolvent and unable to pay, and that she cannot find Bob in order to serve process on him.
E) Sally will lose because Trudy had no obligation to go through with the gift.