Here's why:

* Moving fluid: Blood is a liquid that circulates constantly throughout the body.

* Distributes materials: Blood carries:

* Oxygen: From the lungs to the body's cells.

* Nutrients: From the digestive system to the body's cells.

* Waste products: From the body's cells to the kidneys and lungs for elimination.

* Hormones: From glands to target organs.

* Cells: Like white blood cells that fight infection.

Let me know if you have any other clues or if you're thinking of something else!