How many cells are there between the blood and inside of the alveoli?

Which of these is the most likely consequence of falling petroleum price

Cells destroy body cells infected by a virus or bacteria.

Agene pool: a) is the collection of all the alleles found in a single species b) is the collection of all the alleles found in a single population c) is the collection of all the chromosomes found in a single population d) is the collection of genes in a species that allow the individuals to swim