Caleb had been working with an estate planner for several years prior to his death. Accordingly, Caleb made many transfers during his life in an attempt to reduce his potential estate tax burden, and Caleb's executor, Landry, is thoroughly confused. Landry comes to you for clarification of which assets to include in Caleb's gross estate. Which of the following transactions will not be included in Caleb's gross estate?

a$.$ Caleb gave $$40,000$ to each of his three grandchildren two years ago. No gift tax was due on the gifts.

b$.$ Caleb purchased a life insurance policy on his life with a face value of $$300,000.$ Caleb transferred the policy to his son two years ago.

c$.$ Caleb and his spouse owned their personal residence valued at $$250,000$ as tenants by the entirety.

d$.$ After inheriting a mountain vacation home from his mother, Caleb gifted the vacation home to his daughter to remove it from his gross estate. Caleb continued to use the property as a weekend getaway and continued all maintenance on the property.