Answer: pressure changes
Valves of the heart open and close due to pressure changes
Explanation:
The veins are the blood vessels possessing valves. And because they carry blood away from the heart, the valves helps to prevent back flow of blood due to the low pressure of blood found in the veins.
Thus, Valves of the heart open and close due to pressure changes
<span>B. precipitation</span><span>
The evaporation process uses the sun radiation or sun’s thermal energy for vaporization of a water from the land or soil to be water vapor then in the air. Transpiration on the other hand is the same with evaporation that involves water molecules to be vaporized into the air but it is located in the stoma of the plants. It is like evaporation within plants. This is actually to have homeostasis in plants and still part of the water cycle. </span>
Answer:
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