A closed system is a system that makes no physical or chemical exchanges with its environment. Of these systems provided as choices (tree, human, clock, car), only a clock does not make exchanges with the environment, except for energy.
Therefore, of that list, only a clock would be a closed system.
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No it's an aquifer. trust me because the definition of aquifer is "permeable rock that contains groundwater"
During bleeding, both formed elements (platelets, white blood cells, red blood cells) and plasma are lost from the circulatory system. They are lost proportionally, so initially there is no change in hematocrit.
Hematocrit is the percentage of the blood volume made up of elements (Hct = cell volume/blood volume). During dehydration, only water and electrolytes are lost, and the number of cells remains constant - the same number of cells in a smaller volume leads to an increase in hematocrit. When the body tries to restore blood volume, the first thing to recirculate is water from the ECF and this increases the amount of water without increasing the amount of red blood cells, so the compensatory mechanism causes the hematocrit to fall.
Learn more about Hematocrit on:
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4.6 billion years ago
The study pushes back the clock on the origin of Earth's water by hundreds of millions of years, to around 4.6 billion years ago, when all the worlds of the inner solar system were still forming. Scientists had suspected that our planet formed dry, with high-energy impacts creating a molten surface on the infant Earth.
i hope this helped, have a nice day! (o: