What structure on a compound microscope supports the eyepiece and nosepiece?

The correct choice is indeed the tube. In a compound microscope, the tube serves as a critical structural component that connects the eyepiece (ocular lens) at the top with the objective lenses typically found on the nosepiece at the bottom. This tube is designed to ensure that the light from the objective lenses is directed up through the eyepiece, allowing the viewer to effectively see the magnified image of the specimen being observed.

Moreover, the tube's design helps maintain the proper distance between the eyepiece and objective lenses, which is crucial for achieving the correct focus and magnification of the specimen. Without this structure, the alignment necessary for clear and focused observation would be compromised. The arm, stage, and base, while essential parts of the microscope, serve different purposes; the arm provides support and carries the microscope, the stage holds the specimen, and the base provides stability.