A spherical buoy may be which of the following?

A spherical buoy is commonly used in marine navigation to help indicate locations and guide mariners safely through navigable waters. The choice indicating that a spherical buoy may be lettered is correct because lettered buoys serve as important navigational aids, particularly in systems where letters can convey specific information about navigation routes or points of interest. This type of identification helps mariners easily recognize and remember the buoy's significance in relation to their course.

While it's true that buoys can also be numbered, the specific characteristics of a spherical buoy can include the use of letters for designation in certain buoyage systems, such as the lateral system which uses different markers for navigational routes. The use of colors such as green and red typically distinguishes between different types of buoys (with green often representing starboard and red representing port), but not all spherical buoys are necessarily assigned a color indication.

The use of letters provides a unique advantage in marking specific spots without the need for a numerical system, which may not always be as straightforward for mariners, particularly in complex navigational areas. Therefore, the concept of lettered buoys aligns well with the broader purpose and utility of navigation aids, highlighting their contribution to safe maritime travel.