Which of the following parts of the mature embryo sac start to degenerate after double fertilization?

I) Polar nuclei
II) Antipodal cells
III) Synergids
IV) Central cell

The correct option is D II and III
After the double fertilisation, synergids and antipodal cells start to degenerate since they have no role to play during embryogenesis or endosperm development.

The two polar nuclei fuse with the male gamete to form primary endosperm nucleus (PEN). This is called triple fusion which occurs inside the central cell of the embryo sac.

The central cell of the embryo sac after double fertilisation becomes the primary endosperm cell (PEC). PEC divides repeatedly to form the nutritive tissue, endosperm.