Hint:Double circulation pathways are found in mammals and birds. Animals with this kind of circulatory system have a four-chambered heart. The right chamber receives deoxygenated from the body and the right ventricle sends it to the lungs to be oxygenated.
Complete answer: Transport systems are critical to survive. Unicellular organisms depend on simple diffusion for transport of nutrients and excretion of waste. Multicellular organisms have grown a more developed circulatory system. Double circulation pathways are found in birds and vertebrates and mammals. Animals with this sort of circulatory system have a four-chambered heart.
The right atrium gets deoxygenated from the body and the right ventricle sends it to the lungs to be oxygenated. The left chamber gets oxygenated blood from the lungs and the left ventricle sends it to the rest of the body. Most mammals, including humans, have this kind of circulatory framework. These circulatory systems are called double circulatory systems since they are composed of two circuits, alluded to as the pulmonary and systemic circulatory systems.
Double circulation is the sort of circulation where blood goes to the heart twice. It is fundamentally found in birds, warm blooded animals, and a few reptiles and fishes. Hence, out of the alternatives given in the question, alligator, lungfish, crocodile, birds, and mammals have double circulation.
Therefore, the correct answer is option A, i.e. 'Five'.
Note:Humans, birds, and well evolved creatures like mammals have a four-chambered heart. Fish have a two-chambered heart, one atrium and one ventricle. Amphibians have a three-chambered heart with two atria and one ventricle. The benefit of a four chambered heart is that there is no combination of the oxygenated and deoxygenated blood.