The flowers do not open at all is

Answer: Option A

The flowers do not open at all in Cleistogamy.
Cleistogamy means the formation of flowers that do not open and those flowers are classified as Cleistogamous flowers.
It is a type of automatic self-pollination of certain plants that can propagate by using non-opening, self-pollinating flowers.
Thus the production of seeds in such flowers is a result of autogamy.