Final answer:
All of the options given are examples of systems, including the engine of a car, a living thing, a single water molecule, and the Milky Way galaxy.
Step-by-step explanation:
A system is a group of interconnected elements that work together to achieve a common goal or function. Systems can be found in various fields such as physics, biology, and engineering. In this question, all of the options given are examples of systems.
For example, the engine of a car is a system composed of various components like pistons, valves, and fuel injectors, working together to produce mechanical energy. A living thing, such as a human body, is a complex biological system made up of organs, tissues, and cells that work together to carry out vital functions.
Similarly, a single water molecule can be considered a system as it is made up of atoms bonded together. Finally, the Milky Way galaxy is a highly organized system consisting of stars, planets, and other celestial bodies that interact through gravitational forces.