bone is rigid & something rigid can be used to provide support ->  bones can be used to provide support  bones can be used to provide support & skeletal system is made of bones ->  the skeletal system is used to provide support for animals  something hard can be used for protection & bone is hard ->  bones can be used for protection  bones can be used for protection & skeletal system is made of bones ->  the skeletal system can be used for protection  the skeletal system is used to provide support for animals & the skeletal system can be used for protection ->  the skeletal system can be used for protection and support  the skeletal system can be used for protection and support & if something is used for something else, then that something else is the job of that something -> protection and support are jobs of the skeletal system