How many double circulations are normally completed by the human heart in one minute?

The blood vascular system of mammals is known as a double circulatory system because

Where does the hepatic portal system originate?

Explain in short the mechanism of circulation in living organisms.

The systemic circulation provides nutrients, $A$ and other essential substances to the $B$ and takes $C$ and other harmful substances away for elimination. Choose the correct option for $A, B$ and $C$.

Which of the following carries glucose from the digestive tract to the liver?