Final answer:
Option (b), where Sheila sets up a revocable trust for her daughters, is not a completed gift because she retains the ability to revoke the trust, which signifies that she has not yet released all control over the trust's assets.
Step-by-step explanation:
The option that is NOT a completed gift is (b) Sheila sets up a revocable trust for her 2 daughters. In order for a gift to be considered complete, the donor must relinquish all control and ownership over the property given. Additionally, there must be an actual or symbolic delivery of the gifted property to the recipient, and the recipient must accept the gift.
In the case of a revocable trust, the donor, Sheila, retains the ability to revoke the trust, which means she has not surrendered full control or ownership of the assets within the trust. Therefore, the gift is not yet complete. In contrast, John's transfer of property to his sons in option (a) and Sara's payment of her son's mortgage in option (c) both represent completed gifts because control has been fully transferred and there is no further action required by the donor.