The right answer is vein (it contains blood and has valves).
The infra-cardiac veins of small and medium caliber possess this system of fight against gravity. The valves consist of a dense connective tissue, surmounted by endothelial cells, corresponding to a fold of the intima. They allow blood circulation in the sense organ / heart but prevent venous reflux.
Answer:
predator is blue, prey is red
Explanation:
when the amount of predators increase, the blue line rises, the red line lowers. when there is more predators there is going to be a less amount of prey.
The sustainable use of land means using the spare land in such an activity which supports the society and benefits the environment.
In such a situation if a land is found spare then a park should be constructed on it.
This will create an recreational activity spot for the society and they will be able to spend their leisure time with fun.
Also there will be less pollution and harm to environment will be lowered by greenery and trees in the park.
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