Final answer:
A single layer of epithelial tissues is referred to as simple epithelium, which is characterized by tall and narrow cells with nuclei located close to their basal side, known as simple columnar epithelium. The correct option is A.
Step-by-step explanation:
A single layer of epithelial tissues is known as simple epithelium. In contrast, epithelial tissues with multiple layers are referred to as stratified epithelia.
When observing epithelial cells under a microscope and noting that the cells are arranged in a single layer, tall and narrow, with nuclei located at the basal side, this characterizes simple columnar epithelium.
This arrangement allows such tissue to absorb nutrients and also, if ciliated, move particles across its surface, useful in areas like airways and the lining of the oviduct. The correct option is A.