The skin is the largest organ in the human body.
Why it is true
Covering the entire external surface of the body, the skin acts as a protective barrier against the external environment, regulates temperature, and prevents water loss.
Source: Anatomy
Would you rather be asked first?
This is the reading side of the site, so the answer is in the sentence above — that is the whole point of it. Test yourself works the other way round: the question comes on its own, and the fact and the explanation only appear once you have answered.