Which of the following best describes a system of objects in a frame of reference?

The description of a system of objects within a frame of reference revolves around the relationships and positions of those objects in relation to one another. When considering option B, it denotes that the objects are not moving with respect to one another, which is fundamental in understanding a frame of reference. A frame of reference is essentially a viewpoint or coordinate system from which positions and movements are measured. If the objects are stationary with respect to each other, they can effectively be analyzed together as a coherent system without the complications that arise from their relative motions.

In scenarios where objects move independently or at varying speeds, such as in options A and D, the complexity increases significantly. In such cases, the interactions and relative positions of the objects can change, affecting the analysis of the system. Option C asserts that the objects must be stationary, which is overly restrictive as a frame of reference can also be applied to objects that are in motion, as long as their positions relative to each other are clear. Thus, option B accurately captures the essence of how objects within a frame of reference can be understood when they are not in motion relative to each other, making the concept more manageable for analysis.