The correct option is D By plants themselves
Pollens are yellow coloured powder-like grains produced by stamens and it contains the male germ cell of the flower. Pollen grains, from anthers, get transferred to the female part of the flower, i.e., stigma, the process is called as pollination. They germinate there and later fertilisation takes place where male germ cell fuses with female germ cell and a zygote is formed. Pollination is of two types: self-pollination and cross-pollination. Pollinating agents are animals such as insects, birds, bats, abiotic factors like water, wind and even plants themselves.