From where spermatogenesis starts ?

$A$ : The scrotum acts as temperature regulator for the testes.
$R$ : Wall of scrotum is supported by dartos muscles which help in positioning of testes.

Ostium is provided with a number of finger like processes fimbriae

Given below is a diagrammatic sketch of a portion of human male reproductive system. Select the correct set of the names of the parts labelled $A, B, C, D.$

If the nuclei from an $8$-celled stage of an embryo are transplanted into enucleated eggs, which of the following events is likely to occur