A compound microscope would be the best choice for viewing a piece of moldy bread.

A compound microscope has a series of lenses that magnify the image of an object. The objective lens, which is located at the bottom of the microscope, magnifies the image of the object. The eyepiece lens, which is located at the top of the microscope, then magnifies the image of the object again. This allows for very high magnification of the object, which is necessary to see the details of the mold.

In addition, a compound microscope has a built-in light source that shines light on the object being viewed. This makes it easier to see the details of the mold.

Finally, a compound microscope has a stage that can be moved up and down, which allows you to focus on different parts of the object. This is important for getting a clear view of the mold.

In conclusion, a compound microscope is the best choice for viewing a piece of moldy bread because it provides high magnification, built-in lighting, and a movable stage.