Earth’s inner core is solid because of
a. the composition of its rock.
b. its great diameter.
c. extreme cold.
d. immense pressure.

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.

your answer is going to be physical weathering