Trumpets are hollow unless the part near the tip is solid, and the upper end of some big speakers is solid and can be ejected.

First, rhinoceros horns grow on the nose, with single horns and double horns. Because it grows in the middle of the head, it is closer to a circle or a large ellipse; The horns grow on the forehead and diverge to both sides. Because the cow's forehead is flat, its horns are flat.

Second, all angles have a * * * property, that is, "the former is real and the latter is empty", and "the former is real where the angle refers; Back space "means that the place pointing to the nose or forehead is concave." The older the cow, the longer the hollow and the shorter the solid.