Which conversion factor would best fit in the space labeled “B” in this diagram

This is what i found “nuclear fuel is material used in nuclear power stations to produce heat to power turbines. heat is created when nuclear fuel undergoes nuclear fission. most nuclear fuels contain heavy fissile actinide elements that are capable of undergoing and sustaining nuclear fission.” i hope this you for what your looking for. can you plz mark me brainliest?

Most smaller stars don't have a radiative zone.

I'm not sure but i will try to find out