Which of the following statements refers to a physical property of a substance? a. carbon combines with oxygen to form carbon dioxide. b. the density of copper is 8.93 g/cm^3. c. acids are corrosive. d. zinc metal reacts with an acid to produce hydrogen gas.

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.