The correct option is D Cleistogamy
Autogamy or self pollination is a kind of pollination in which the pollen from the anthers of a flower are transferred to stigma of the same flower. Cleistogamy, homogamy and chasmogamy are the methods of the autogamy. Cleistogamy occurs in those plants, which never open and ensure complete self–pollination. E.g., Commelina Oxalis, Viola, etc. In self-pollinating flowers, pollination typically occurs when the flower is open with its anthers and stigma exposed. This type of pollination is called chasmogamy. In homogamy stamen and the pistil mature at the same time to facilitate self pollination.