Which of the following areas in a secondary lymphoid organ allows intimate contact between blood and the lymphocytes?

red pulp of the spleen
germinal centers of the lymph nodes
Hassall's corpuscles of the thymus
white pulp of the spleen

a- multicellular

b-eukaryotic

c-no cell wall

d-heterotrophic

e-autotrophic

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.