What are the diploid stages in gametogenesis?

The correct option is B Spermatogonia and primary spermatocytes
Spermatogenesis is the process of formation of spermatid(n) from spermatogonia$\left(2n\right)$. The process goes as follows:-

Spermatogonia$\left(2n\right)⟶$ Primary Spermatocyte$\left(2n\right)⟶2$ Secondary Spermatocyte$\left(n\right)⟶4$ Spermatid$\left(n\right)⟶4$ Sperms$\left(n\right)$

The only diploid stages are the spermatogonia and primary spermatocytes.

So the correct answer is B.