Although individual body systems can perform specific functions, they depend on one another and work together for the good of the entire organism. Which of the following provides the best evidence that the digestive system and the muscular system work together to carry out their functions ?
A : Muscles help move food through the body to the stomach.
B : Messages from the brain tell the body how to move.
C : Oxygen is transferred through the body by the bloodstream
D : Lungs expand and contract through movement of the diaphragm muscle