Is this a gratuitous promise?

A high school student was deciding which college she would attend the following year. Her grandmother told her, "If you will follow in my footsteps and attend my alma mater, there will be a shiny new sports car waiting in the driveway on the day you graduate." The granddaughter promised to consider the offer. She did eventually enroll at her grandmother's alma mater but only because of a very attractive scholarship offer, coupled with the fact that her current boyfriend was planning to attend. Several weeks prior to the student's graduation, the grandmother died. Her will made no mention of any gift to her granddaughter.

Immediately after her graduation, the student sued her grandmother's estate for the cost of a popular sports car. What is the most likely result?

(A) The student will win, because she fulfilled her part of the bargained-for exchange. (B) The student will win, because she relied to her detriment on her grandmother's promise. (C) The student will lose, because her grandmother's promise was gratuitous. (D) The student will lose, because no specific car was selected and agreed upon