yes 2D. thank you!
because it is so simple just two pic exchange both.
so, I set two states in a FSM on the game object,
state A:
set Material texture use textureA
wait 1 sec
state B:
set Material texture use textureB
wait 1 sec
and, I can do it 2-3 year ago with old unity, but nowadays updated unity to 2019.2 then it doesn't work.
thank again!