Damage to which body system would most directly affect the body's ability to receive oxygen from the environment? a. digestive b. nervous c. respiratory d. circulatory

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.