Concerning Guardians

Hey guys I'm a bit confused about Guardians forgive me for the noob question.

I notice that when I have multiple Guardians in a battle, they sometimes all activate their aoe shields at once, which confuses me because I don't understand how this mechanic can work.  I know with one, 33% of the damage your units take goes against the Guardian's shield reserves, but what happens when you have multiple aoe shields up at once?

Is it

A) The Guardian with the highest amounts of shields is the only one affected.

B ) The Guardians spread the damage evenly among themselves as if the shields were connected.

or

C) Nothing happens until a Guardian's shield reaches 0, at which point it switches to the next Guardian.

Any help on this question would be appreciated.  Thanks guys.