Which of the following are post-fertilization events?

Both (a) and (c)

a- Formation of endosperm

b- Formation of megaspores

c- Development of embryo

d-Both (a) and (c) is the correct option.

The correct answer is (d) Both (a) and (c) - Endospermogenesis and embryogenesis are both post-fertilization events.

1. Endospermogenesis: After fertilization, the primary endosperm nucleus (PEN) resulting from the fusion of the two polar nuclei and one male gamete  undergoes several rounds of divisions resulting in the formation of endosperm. This endosperm provides nourishment to the developing embryo.
2. Embryogenesis: After fertilization, the zygote undergoes a series of mitotic divisions and differentiation to develop into an embryo. These divisions and differentiation processes lead to the formation of different embryonic structures such as the shoot apical meristem, root apical meristem, cotyledons, and embryonic axis.

Both endospermogenesis and embryogenesis are crucial steps in the development of seeds in flowering plants. The endosperm provides nutrients for the developing embryo, while the embryo develops into a mature plant.