sentences: muscles push / pull bones to move the bones & the muscular system contains muscles ->  the muscular system push / pull bones to move the bones  the muscular system push / pull bones to move the bones & skeletal system is made of bones ->  the muscular system push / pull parts of the skeletal system to move the skeletal system  moving parts of something helps to move that something & a skeletal system is a part of an animal ->  moving an animal's skeletal system helps to move that animal  the muscular system push / pull parts of the skeletal system to move the skeletal system & moving an animal's skeletal system helps to move that animal ->  the muscular system moves the skeletal system to help an animal move  the muscular system moves the skeletal system to help an animal move & if things are used in a process, then those things are involved in that process -> the muscular system and the skeletal system are involved in helping an animal move