The right answer is A.
Apoptosis is cell suicide, or programmed cell death (according to an established genetic program). the opposite of necrosis which is a cell death due to a toxin.
Thus, it is the apoptosis that kills the cells between the fingers during the embryonic development, to allow to dissociate them. The same phenomenon makes the caudal appendage disappear.
Apoptosis is also involved in the elimination of incompetent or useless immune cells.
Apoptosis is also used to eliminate cells that have irreparable damage to DNA (damaged telomeres), to prevent the development of cancer.