At the time of Emile's death, he was a joint tenant with Colette in a parcel of real estate. With regard to the inclusion in Emile's gross estate under § 2040, comment on the following independent assumptions:

a. Emile and Colette received the property as a gift from Douglas.

b. Colette provided the entire purchase price of the property.

c. Colette's contribution was received as a gift from Emile.

d. Emile's contribution was derived from income generated by property he received as a gift from Colette.