The correct option is
D Spermatid to sperm
Spermatogenesis is the process of formation of spermatid(n) from spermatogonia
(2n). The process goes as follows:-
Spermatogonia (2n)⟶ Primary Spermatocyte ⟶Secondary Spermatocyte(n)⟶ Spermatid (n)
Spermiogenesis is the metamorphosis of spermatid into sperm.
So the correct answer is D.