Which solid has an infinite number of planes of symmetry?

A solid hollow cylinder has an "infinite number of planes of symmetry".

Explanation:

Two or more faces are said to be symmetric when they have the same dimensions and are geometrically identical. When these faces are placed in a setting with 'X', 'Y' and 'Z' axes "perpendicular to each other", they make a plane with three lines of symmetry. A circle has "infinite lines of symmetry". Thus, a cylinder with two openings has an "infinite number" of "planes of symmetry".