What substances are involved in controlling the production of sperm and eggs in humans? Hormones.
C. because there is a property of acids which stat that they turn litmus papers red instead of blue.
Answer: Possession of Valves
Explanation: Veins possess valves which ensures that blood flows in only one direction. Valves helps blood to flow back to the heart against gravitational force.
Arteries don't have valves because the pressure originating from the heart is capable of causing the blood to flow in one direction.