One characteristic of enzymes is that they are reusable. This is important
because

i think that d. wind is the answer.   i missed the question when i answered a. currents.

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.