Which organ is the body's largest and forms the external protective layer?

• A. Skin
• B. Bones
• C. Brain
• D. Lungs

Answer: (A)

Skin is the body's largest organ and forms the external protective layer. It covers every part of the body, acting as a physical barrier that reduces injury, blocks pathogens, and helps prevent water loss. In addition to protection, the skin helps regulate temperature, enables the sense of touch through nerves, and houses immune cells to defend against invaders. Its structure—epidermis on the outside, with the dermis underneath and a fatty hypodermis beneath that attaches to deeper tissues—allows it to perform these roles effectively. The bones provide internal support, the brain is the control center of the nervous system, and the lungs handle gas exchange; none of these form the外 protective shell that covers the body. So, the skin best fits being the largest organ and the external protective layer.