The spindle fibres start appearing from stage of karyokinesis. 1. prophase
2. methaphas
3.araphase
4. telophasa​

methaphas is the answer

[A] Prophase.

In metaphase, the microtubules pull the sister chromatids and align them in the equatorial plane. In anaphase, the sister chromatids get separated due to the pulling by the spindle fibers. Therefore, the stage of karyokinesis, the spindle fibres start appearing is prophase.

"it built up in the atmosphere"

i think thats it, idk, i tried looking for this exact q& a for grad. and idk if i got this question right or sorry if im wrong