30. carry oxygen rich blood from the heart to the body's tissues and organs. choices: veins, arteries, capillaries or alveoli

Arteries. Arteries carry oxygen-rich blood away from the heart to all of the body's tissues. They branch several times, becoming smaller and smaller as they carry blood farther from the heart and into organs.

Capillaries. These are small, thin blood vessels that connect the arteries and the veins. Their thin walls allow oxygen, nutrients, carbon dioxide, and other waste products to pass to and from cells.

Veins. These are blood vessels that take blood back to the heart; this blood contains less oxygen and is rich in waste products that are to be excreted or removed from the body. Veins become larger as they get closer to the heart. The superior vena cava is the large vein that brings blood from the head and arms to the heart, and the inferior vena cava brings blood from the abdomen and legs into the heart.

Any of the many tiny air sacs of the lungs which allow for rapid gaseous exchange are called alveoli.