Humans have altered the water cycle by

A) digging up the stored nutrient resources and combusting them during industrial processes.

B) damming rivers and lakes.

C) increasing the rate at which land based nitrogen is released into the environment.

D) all of the above

the supermassive black hole is in the middle of the galaxy.

the principles and empirical processes of discovery and demonstration considered characteristic of or necessary for scientific investigation, generally involving the observation of phenomena, the formulation of a hypothesis concerning the phenomena, experimentation to test the hypothesis, and development of a conclusion that confirms, rejects, or modifies the hypothesis.

answer; both surfaces of the membrane are nonpermeable

the answer is true when observing or determining population size, a direct observation is use, in which each organism is counted in a population or in an area. one benefit of this measure is that you get the exact population count but it will take a long time to  determine  the  size  of a  population.