It is A
From the Fearless rule, highlighted the relevant part.
Quote:
2.1.3 Fearless
Some units are noted as being fearless. Such units are either exceptionally brave or so crazed that they will never run away even when broken (though you can choose to have them make a withdrawal move if you want them to). Units that are Fearless are immune to damage from losing an assault (both the additional hits and being wiped out if already broken) and from the damage inflicted by Blast markers if broken. When broken or otherwise forced to take a withdrawal move, Fearless units may choose not to withdraw, and if the
unit elects to withdraw it will be destroyed only if it ends its move within 5cm of the enemy rather than 15cm. Fearless units that remain stationary do not take additional damage. Note that other units in the formation that are not fearless will be affected normally by additional hits for Blast markers or losing an assault or whatever – just don’t allocate any of the hits to the units that are immune, but hand them out as normal to units that are not.
