When I first saw it, the water surface had a certain height, and the water surface rose with the stones. After drinking water, the water level drops, but the falling water level is always higher than the initial water level.

Interviewee: peterxbj | level 4 | 2010-12-110: 22

First, crows don't drink water, and the water level remains the same for some time. Later, he thought of putting stones in it to make the water level rise, but the shape of the bottle made the water level rise change with time. The bottle is narrow at the top and wide at the bottom, and the water level rises slowly first and then quickly. Then the crow drinks water and the water level drops. Choose D.