How is a lake or river that freezes over to the organisms in the water?

with pass cost = $25

without pass cost = 3x number of days going the the class

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.