Which of the following are true about the interactions between or among the integumentary, muscular, and skeletal systems of the human body?
I. The skin of the integumentary system protects the muscles of the muscular system and the bones of the skeletal system from the outside environment.

II. The muscles of the muscular system contract or relax to move the bones of the skeletal system.

III. The bones of the skeletal system and the skin of the integumentary system work together to provide protection for the human body.