Please help me with these muscle and bone questions ASAP.

Bones' hardness is made up of ________. Bones' crystals, layered for strength, gradually dissolve and are carried away by the bloodstream. They are replaced every ______.

The ______ is the most massive because it must support the upper torso and protect the spinal cord. It contains ______ vertebrae, separated by soft discs, and ends at the ______.

Muscles are "fired" _____, the action of coming from the attraction of different protein in their fiber. Muscle cells are as thin as hair and some are to _____ long. For maximum effort, muscles produce energy which doesn't require _____. _____ build-up causes pain and fatigue.