Read the excerpt from The Time Traveler's Guide to Elizabethan England. The theory of the humors is just the basic framework into which physicians fit a number of other ideas. Galen teaches that every living thing is composed of the four elements: fire, earth, air, and water. Each of these corresponds with one of the four humors. Fire, which is said to be hot and dry, corresponds with choler; water (cold and wet) with phlegm; earth (dry and cold) with black bile; and air (hot and wet) with blood. These properties are all associated with parts of the body, so the brain is cold and moist, the kidneys hot and moist, and so on. If an imbalance in the humors clashes with the properties of an organ, the patient will be ill.

Which sentence best summarizes the excerpt?