Some complex multicellular organisms are organized at four levels to increase efficiency. what is the correct order of organization, from the simplest to the most complex? a. organ, tissue, cell, organ system b. cell, organ, organ system, tissue c. tissue, cell, organ system, organ d. cell, tissue, organ, organ system

The correct answer is D. 

The cell is the smallest structure and functional unit of an organism. Our bodies are made up of little cells. When enough of the same cells are grouped together, they create a tissue. When there is enough of the same tissue, it creates an organ. Finally, when there are enough cells that make enough tissue that make enough organs, these organs then work together in an organ system.