The existence of a sterile neutrino is a possible explanation for the pulsars whizzing through the universe at high speeds.
A – Wrong
This statement is too strong as it says “Sterile neutrinos must be the cause of the phenomenon”.
The word ‘must’ is too strong.
B – Correct
This uses the appropriate words “could be caused by the existence of sterile neutrinos”.
C – Wrong
Again “best explanation” is too strong to use as we have not heard any other hypotheses.
D – Wrong
Again, this statement is too strong. D is effectively stating that sterile neutrinos are definitely the cause of pulsars.