The atmosphere is an example of an exchange pool for water

white blood cells or wbc s are mainly 2 types-

1.agranulocytes

2.granulocytes

the monocytes or macrophages of agranulocytes , dendritic cells which are accessory leucocytes, and b cells which is one type of lymphocytes   identify the antigens present on the pathogen's surface. these three cells are called antigen presenting cells(apc) which are phagocytes and destroy the antigens by secreting antitoxins. besides this leukocyte is always plays vital role in the immunity of the body.

i think it is dna, i'm not totally sure but i think it might be.

a. by using fur or clothes to trap heat energy near the body

the answer you are looking for is the united states forest service.

hope this !