Her immune system is exhibiting the _ line of defense. this defense is part of _ immunity.

last line of defense is the first part.

and the defense is part of her system immunity. this makes sense since the immune system is used to guard against viruses and diseases

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.