Question

what are capillaries?
small tubes that carry air from the lungs to the rest of the body.
thin fibers that make up muscles in the body.
tiny blood vessels that connect arteries and veins and allow for the exchange of gases and nutrients between the blood and the surrounding tissues.
a type of white blood cell that fights infection.
a type of bone found in the human body.

Explanation:

Capillaries are part of the circulatory system. They are the smallest blood vessels. Their main function is to connect arteries (which carry oxygen - rich blood away from the heart) and veins (which carry oxygen - poor blood back to the heart). At the capillary level, there is an exchange of oxygen, carbon dioxide, nutrients, and waste products between the blood and the surrounding tissues.

• The first option is incorrect as the tubes that carry air are part of the respiratory system (like bronchioles), not the circulatory system where capillaries are.
• The second option refers to muscle fibers (myofibrils), not capillaries.
• The fourth option refers to white blood cells (leukocytes), which are cells in the blood, not vessels.
• The fifth option refers to bones, which are part of the skeletal system, not the circulatory system.

Answer:

Tiny blood vessels that connect arteries and veins and allow for the exchange of gases and nutrients between the blood and the surrounding tissues.