Can you guess this science riddle?

Rocks do not float. When the rock is in the boat, the water displaced is proportional to mass. When the rock is on the bottom of the water, the water displaced is proportional to the volume of the rock.

Answer D: Not enough information (rock density needed)

edit: rock density is higher than water density, therefore it's answer A, the water level rises. (Not enough info to determine the amount)

edit2: what a mess! The displaced water pushes the water level up, not down. Less displaced water, therefore lower water level. B