Work Step by Step
Option b. is incorrect. The lymph nodes are bean-shaped structures throughout the body and connected to the lymph vessels that collect and destroy pathogens and cancer cells. Option c. is incorrect. Capillaries are tiny blood vessels that are the sites of exchange of nutrients, gases, and waste products. Option d. is incorrect. The bronchioles are small tubes that branch off from larger bronchi and transport air to the alveoli. Option a. is correct. Alveoli are tiny air sacs located in the lungs and are the sites of gas exchange.