Read the following statements and answer the question.
  1. It is made of a single thin layer of flattened cells with irregular boundaries.
  2. They are found in the walls of blood vessels and air sacs of lungs.
  3. 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. Squamous epithelium

B. Columnar epithelium

C. Ciliated epithelium

D. Compound epithelium

Please do not use chat terms. Example: avoid using "grt" instead of "great".