Sweat is made by very many—maybe several million—little sweat glands scattered around your skin. They are more tightly packed on the palms of your hands and the soles of your feet. When seen in a microscope, each gland looks like a coiled-up tube with an opening on the surface of the skin. Its job is to make sweat. Sweat evaporates from the skin and cools your body. Which best describes the main idea of the passage?
A.
the purpose of skin
B.
the skin on feet and hands
C.
how to use a microscope
D.
how sweat glands work