Question

which of the following allow red blood cells to flow through one cell at a time or single file?
a arteries
b ventricles
c aorta
d atrium
e capillaries
question 18
what stops blood from flowing back into the atrium from the ventricle?
a the two chambers are not connected.
b the blood naturally will follow the path of least resistance.
c the one - way atrioventricular valve located between the two compartments.
d the pressure from the atrium keeps the blood in the ventricle.

Explanation:

For the first question: Capillaries are the smallest blood vessels, with a diameter similar to a single red blood cell, forcing red blood cells to flow in single file. For the second question: Atrioventricular valves (e.g., mitral, tricuspid) between atria and ventricles open to let blood flow from atrium to ventricle and close to prevent backflow.

Answer:

E. capillaries
C. The one-way atrioventricular valve located between the two compartments.