The phenomenon of maturation of anthers earlier than the stigma of the same flower is
Heterostyly is the occurrence of 2-3 types of flowers within the same plant. Such flowers have a difference in length of styles and stamens.
Protandry is the condition when anthers mature before the stigma becomes receptive is called protandry. So, the condition in which the male reproductive organs of a flower mature before the female ones, and hence ensuring that self-fertilization does not occur.
Dicliny is the presence of only one kind of reproductive whorl in a flower.
Herkogamy is the condition in which the flower structure is such that even being bisexual. In some flowers, a mechanical barrier exists and thus self-pollination is not possible. Sometimes, there is a hood for covering the stigma.
So, the correct answer is B.