6)Why do the walls of the stomach secrete hydrochloric acid? 7)Which TWO parts of the alimentary canal make up the small intestine?

The table below shows the elements that mainly comprise each of the four layers of earth: elements in layers layer main elements crust oxygen, silicon mantle iron, magnesium outer core iron, nickel inner core iron which of these elements make up the layer that is 0.2 to 1.1 percent of earth's total diameter?