What Mechanism Is Used to Prevent Self-Pollination in Angiosperms

What mechanism is used to prevent self-pollination in angiosperms?

A) separating male and female individuals
B) shedding of pollen when the stigma of that flower is receptive to pollen
C) separating male and female flowers
D) preventing a plant form recognizing its own pollen with self-incompatibility genes
E) stimulating growth of the pollen tube with self-incompatibility genes