Rigid skeletons are formed from materials including chitin (in arthropods), calcium compounds such as calcium carbonate (in stony corals and mollusks) and silicate (for diatoms and radiolarians).
Rigid skeletons are formed from mostly of collagen, bone is living, growing tissue. Collagen is a protein that provides a soft framework, and calcium phosphate is a mineral that adds strength and hardens the framework. This combination of collagen and calcium makes bone strong and flexible enough to withstand stress.
Uhh her parents I guess? not really a doctor you should talk to because that’s just growing up for women.. all of them get their periods, it’s not abnormal
<h2><u>its is (A) skeletal and muscular</u> </h2><h2>because without skeletal ur body want be able to move also the muscular system do the sam but it give u strength to move it.</h2>
