In American Mah Jongg, which player would have the right to proceed?

Question

We are playing MJ with 14 tiles- discard then pick.
Player A discards tile, Player C calls tile, HOWEVER, next player, Player B calls Mah Jongg (not using discarded tile) at the exact time that Player C calls discarded tile. Does play resume with player C getting tile for exposure or does the Mah Jongg of Player B take precedence as win?

Answer 1

Player A

Answer 2

player a