It is found in the wall of blood vessels.

The tissue that has a free surface,which may contain either cilia or microvilli,is:

........ is found in the lining of the stomach and intestine.

Read the following statements and answer the question.
$(i)$ It is made of a single thin layer of flattened cells with irregular boundaries.
$(ii)$ They are found in the walls of blood vessels and air sacs of lungs.
$(iii)$ They are involved in functions like forming a diffusion boundary.
Which of the following characteristics of tissue is being described by the above statements?

$A$ group of cells is called $...........$.

Ciliated epithelium in vertebrates is present in