Which of the following charitable contributions, if not transferred in trust, would be considered a gift of less than the donor's entire interest and, thus, not currently deductible?
a. A gift of an undivided remainder interest in a personal residence
b. A gift of an undivided remainder interest in artwork
c. A gift of an undivided remainder interest in real estate granted solely for conservation purposes
d. A gift of an undivided one-half interest in artwork