Fill in the blanks:
$(a)$ Cork cells possess ........... on their walls that make them impervious to gases and water.
$(b)$ .................. have tubular cells with perforated walls and are living in nature.
$(c)$ Bone possesses a hard matrix composed of ............... and ............. .

(A) Suberin: It is a waxy substance deposited in the cell walls of cork cells,making them impermeable to water and gases.
$(b)$ Sieve tubes: These are components of the phloem tissue,consisting of living tubular cells with perforated end walls (sieve plates).
$(c)$ Calcium and phosphorus: The matrix of bone is rich in calcium and phosphorus salts,which provide strength and rigidity to the skeletal system.