I think your answer should be B. an organism. Hope this helps. =^-^=
There are 3 sources of calories (or energy), which are also known as macronutrients: carbohydrates, protein, and fat. Of these three, carbohydrates are the body's preferred source of energy. Carbohydrates break down into glucose, which is an immediate source of energy especially for the brain and muscles.
Unicellular organism: prokaryotic organisms and eukaryotic organisms
The earth-moon relationship is unique in many ways. It is the largest moon in the solar system relative to its host planet. The relative size between theearth and moon are so close, some refer to it as a binary planet system. As it is simply a a relationship between a planet and its moon, the system is called a binary system.
