Mater, a wealthy widow, wishing to make a substantial and potentially enduring gift to her beloved adult stepson Prodigal, established with Vault Savings and Loan Association a passbook savings account by an initial deposit of $10,000."For this question only, assume the following facts. The passbook was issued by Vault to Mater solely in her own name. That same day, disinterested witnesses being present, she handed the passbook to Prodigal and said, "As a token of my love and affection for you, I give you this $10,000 savings account." Shortly thereafter, she changed her mind and wrote Prodigal, "I hereby revoke my gift to you of the $10,000 savings account with Vault Savings and Loan Association. Please return my passbook immediately. Signed: Mater." Prodigal received the letter but ignored it, and Mater died unexpectedly a few days later. In litigation between Prodigal and Mater's estate, which of the following is a correct statement of the parties' rights with respect to the money on deposit with Vault?
The estate prevails, because Mater's gift to Prodigal was revocable and was terminated by her death.  The estate prevails, because Mater's gift to Prodigal was revocable and was terminated by her express revocation.  Prodigal prevails, because he took Mater's claim to the savings account by a gratuitous but effective and irrevocable assignment from Mater.  Prodigal prevails, because his failure to reject the gift, even if the assignment was revocable, created an estoppel against Mater and her estate