$(a)$ Why are complex tissues called so?
$(b)$ Why is connective tissue called so?
$(c)$ What is the function of the tissue present in the lining of kidney tubules?

(N/A) Tissues that are made up of more than one type of cell,which work together to perform a common function,are called complex tissues.
$(b)$ Connective tissue is named so because its primary function is to bind,support,and connect different tissues and organs of the body together.
$(c)$ The lining of kidney tubules is composed of cuboidal epithelium,which provides mechanical support and helps in absorption and secretion.