The correct options are
A One kidney
D A part of the liver
Living donors potentially can donate one of the two kidneys. A kidney is the most frequently donated organ from a living donor. The donor's remaining kidney provides the necessary function needed to remove waste from the donor's body for the rest of his/her life. A part of the liver can also be donated by a living donor as the liver is capable of regenaration. Other organs like heart, brain, etc. cannot be harvested from a living donor.