Epithelial tissue forms membranes that cover the body, as well as lines body cavities and glands. Simple squamous epithelium consists of thin, flattened cells, that are one layer thick and allow for the easy movement of substances. This is especially important for gas exchange in the alveoli of the lungs and in the capillaries of the body. The minimal barrier provided by simple squamous epithelium allows molecules to easily diffuse across the membranes.

Stratified squamous epithelium is many layers thick and forms the skin and lining of mucous membranes. Simple cuboidal epithelium functions in absorption and secretion in the kidney tubules and salivary glands. Simple columnar epithelium forms a thick layer that lines the esophagus, stomach, intestines, and uterus. Pseudostratified columnar epithelium possess beating cilia and transport particles in the respiratory tract and reporductive system. 

Ciliated epithelium are located in the respiratory tract. There are hair-like processes, cilia, located on the surface that wave and function to sweep materials, such as mucous and dust, across the surface. Cuboidal epithelial calls are as high as they are wide. Cuboidal cells line the ducts of glands and organs and function in the absorption and transportation of substances. Squamous epithelial cells are flat and allow substances to freely move across their surface. These cells are located in the lungs and the kidneys. Stratified epithelial cells form layers, with mitosis taking place in the lowest layer. Skin is formed from stratified epithelial cells. Transitional epithelial cells adjust to mechanical changes such as stretching. This type of tissue is found only in the urinary system.

Keratinized stratified squamous epithelium makes up the outer layer of skin. Other types of epithelial tissues are found throughout the digestive and reproductive tracts, and other areas of the body.

Since capillaries are the site of diffusion of substances (oxygen and carbon dioxide, for example), they need to have extremely thin walls. Their walls are made of simple (single-layered) epithelium. The other options would be too thick to facilitate diffusion of substances.

Since we are looking for a single layer of cells, we must rule out any area of the body that is subject to lots of friction. The skin is continually being rubbed and pushed by everything we touch, and the esophagus sustains abrasions from all the food we eat.

Microvilli are tiny projections on the apical surface of cells that increase the cell surface area. Since most of the absorption of food and nutrients occurs in the small intestine, it makes sense that we would want to increase the surface area of that region. Furthermore, since we are absorbing, we would want a single layer of cells to facilitate the diffusion of substances across the layer of epithelium. Thus, the correct answer is that simple columnar epithelium with microvilli will be found in the small intestine.

All of these areas of the body are subject to lots of friction. Thus, there would be multiple (stratified) layers of epithelium lining them.