An inverted right circular cone with height 30 cm and base radius 15 cm is being filled with water at a constant rate. Which of the following best describes how the rate at which the water level rises changes as the depth of the water increases?
a) dh/dt decreases as h increases because each extra centimeter of depth requires more volume.
b) dh/dt remains constant since the inflow rate dV/dt is constant.
c) dh/dt increases with depth because the growing column of water is heavier and pushes the surface upward faster.
d) dh/dt first increases and then decreases because the cone widens and then narrows.