A rabbit eats 25 grams of grass. A half hour later, Joe weighs the rabbit on a scale. Its mass is only 18 grams more than it was before it ate the grass. Which of the following best explains what happened to the other 7 grams of mass ?

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.