These are the only vertebrates in which blood flows directly from respiratory organs to body tissues without first returning to the heart.
A)Amphibians
B)Birds
C)Fishes
D)Mammals
E)Reptiles

Question

Quizplus · Accepted Answer

Fishes have a single-loop circulatory system where blood flows from the gills to the body tissues without returning to the heart. This allows for efficient oxygen uptake from the water and is why many aquatic animals have gills instead of lungs.

These Are the Only Vertebrates in Which Blood Flows Directly