Four friends talked about the human body. They each agreed that the cell is the basic unit of structure in the human body. But they did not agree on the basic unit of function in the human body.

A: Seif: I think organs are the basic unit of function. B: Juanita: I think tissues are the basic unit of function. C: Sarah: I think body systems are the basic unit of function. D:Todd: I think cells are the basic unit of function in the body.

Explain your thinking.