Recent Research Has Shown That Pollination Requires That Carpels Recognize

Recent research has shown that pollination requires that carpels recognize pollen grains as "self or nonself." For self-incompatibility, the system requires

A) rejection of nonself cells.
B) the rejection of self cells.
C) carpel incompatibility with the egg cells.
D) that the flowers be incomplete.
E) the union of genetically identical sperm and egg cells.