1000 grams are in one kilogram
The answer is D. The natural selection is a theory which illustrates the gradual process of evolution in the population due to the change of environment. The key point is the mutation (variation) exists in the population before the environment changing. For C, if the environment does not change, though the adaptation is useful to environment, it will not be selected. Because the organisms without the adaptation will not die.
Because it is polar and it is to large to cross the membrane and because the concentration gradients are to strong so they have to be diffused.
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D. All of the above are true.
