Q 488

A spellcaster is hit by an arrow while casting a spell...

A) If the arrow does two separate sets of damage (for example, from a flaming bow), must the spellcaster roll separate concentration checks (one for the piercing damage, one for the fire damage), or are all the damage taken in account for the same check?

B) What if the arrow is poisoned and the spellcaster fail the saving throw? Does ability damage count as "damage dealt" for a concentration check? Is it a separate concentration check from the arrow damage itself?

C) What if the arrow inflict 0 hp of damage thanks to damage reduction? Does the caster still need to roll a concentration check?
(The question can also apply to an area effect with a caster taking 0 damage thanks to Evasion...)