Faster and better growth of pollen from other plants than the pollen from the same plant is?
Self-incompatibility is the widespread mechanism in flowering plants which prevents the inbreeding and promotes the outcrossing. Dichogamy is the mechanism when the stigma and anther mature at different times. Monocliny i.e. Bisexuality is applicable for bisexual flowers. Pollen prepotency is the mechanism when the pollen of a different flower germinates faster than of the same flower thus preventing autogamy.
Thus, the correct option is D.