Correct Option: A

Chitin is the main component of the cell walls of fungi, the exoskeletons of arthropods such as crustaceans (e.g., crabs, lobsters and shrimps) and insects, the radulas of mollusks, and the beaks and internal shells of cephalopods, including squid and octopuses. Combined with calcium carbonate, as in the shells of Crustacean and mollusks, chitin produces a much stronger composite.