The correct answer is D) whether the number is odd or even. The preferred channel at a bifurcation is not indicated by the number of the buoy, whether it is odd or even. The preferred channel is typically indicated by the color and shape of the buoy, as well as the color of the light (if it is a lighted buoy). The number on the buoy is used for identification purposes, not to indicate the preferred channel. The other options are incorrect because the color of the light, the color of the topmost band, and the shape of an unlighted buoy are all used to indicate the preferred channel at a bifurcation, but the number on the buoy is not.