What type of circulatory system is present in a frog?

What is the system called where blood vessels originate in capillaries and end in capillaries?

The hepatic portal vein carries blood to the liver from the ..........

Double circulatory heart is present in

In amphibians and reptiles,the $A$ atrium receives oxygenated blood from the gills/lungs/skin and $B$ atrium gets the $C$ blood from other body parts. Choose the correct option for $A$,$B$,and $C$.

Systemic circulation is: