Which of these processes involve separation of grains? A)Tilling
B)burrowing action of earthworm
C)Levelling
D)Both a nd b

b tumor cells have a cell wall instead of a membrane

explanation:

tumor cells different from normal cells because tumor cells have a cell wall instead of a membrane.

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.