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.
The answer is D. in animal cells, the cell membrane allows materials in and out of the cell, while the mitochondria uses nutrients to make energy (ATP) for the cell.
weight=mass*gravitational accelaration
we know the weight and the gravitational acceleration
400N=m*10m/s^2
m=400N/10m/2^2
m=40kg
Answer: 1, 2, 5 is the correct answer
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Explanation: