What is a sheet of areolar tissue that usually contains fat and attaches the dermis to underlying structures.?

The correct answer is Superficial fascia.

The superficial fascia is a thin sheet of loose connective tissue that lies between the skin and the deep fascia. It is composed of collagen and elastic fibers, and it contains blood vessels, nerves, and lymphatic vessels. The superficial fascia also contains fat cells, which give it a soft, cushioning texture.

The superficial fascia helps to hold the skin in place and protect the underlying structures from injury. It also allows the skin to move smoothly over the underlying muscles.