D. population and nutrients
"What is human nature?" is the key question psycology seeks to answer
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.
Absorption is when the root absorbs water from the soil and transfers it through the xylem. Transpiration is when the water leaves the leaf surface. The water reaches the leaves through xylem
