I'm going to provide different examples, so you can pick whichever ones sound smart.... Anyone is welcome to correct me...
Function: Blood flow
Explanation: The heart pumps blood throughout the body through different sized tubes called veins and arteries.
Function: Provide oxygen
Explanation: The blood carries oxygen from the lungs to the rest of the body, and collects the carbon dioxide to release from the lungs after every breath.
Function: Transports blood
Explanation: The blood is made of different parts- red blood cells, white blood cells, and plasma. The red blood cells get to play with the Oxygen and C02, while the white blood cells get to fight off the viruses and whatever else is in your blood that shouldn't be. The plasma is the liquid that allows your blood to flow without sticking to the sides of the vein.
Function: Regulate body temperature
Explanation: The blood is causing a sort of friction in your vessels that keep you warm on the inside. Blood is naturally warm, like how you know you are blushing because your cheeks feel warm? The blush is just excess blood flow to your cheeks.