$(a)$ What is the role of mucus in the stomach?
$(b)$ How is the exit of food from the stomach regulated?
$(c)$ Where does food enter from the stomach?

(N/A) Mucus protects the inner lining of the stomach from the action of the acid under normal conditions.
$(b)$ The exit of food from the stomach is regulated by sphincter muscles,which release it in small amounts into the small intestine.
$(c)$ From the stomach,food enters the small intestine.