Can an unfertilised,apomictic embryo sac give rise to a diploid embryo? If yes,then how?

(A) Yes,an unfertilised,apomictic embryo sac can give rise to a diploid embryo.
This occurs through a process called diplospory or apospory.
In diplospory,the megaspore mother cell undergoes mitosis instead of meiosis,resulting in a diploid embryo sac.
Consequently,the egg cell within this embryo sac is diploid $(2n)$.
This diploid egg cell then develops directly into an embryo through mitotic divisions without undergoing fertilisation,a process known as parthenogenesis.