The universe consists of many different galaxies, which, in turn, consist of many different solar systems. Each solar system has a central star around which planets orbit. Earth, for example, is a planet that orbits the Sun in the Solar System. The Solar System is one of many that can be found in the Milky Way galaxy. This example demonstrates that
A. some systems contain other smaller systems.
B. some systems are a part of larger systems.
C. some systems are connected to other systems.
D. all of these