After putting a stone in, some water overflowed, and then taking it out, the water level dropped by 4 cm.

It is proved that the volume of stone = overflowing water.

Volume of overflow water = length * width * height (the height of overflow water here is 4cm).

So the volume of stone =20* 15*4= 1200 cubic centimeters.

A: The volume of the stone is 1200 cubic centimeters.