Which is the best definition of directional selection? a process by which two species can no longer reproduce
a process by which one of the extreme variations of a trait is favored
a process by which individuals with either extreme of a trait are favored
a process by which average individuals in a population are favored

B. a process by which one of the extreme variations of a trait is favored

Explanation:

The graph for this type of selection looks sort of like a camel's hump. With that being said, the phenotype of a population experiencing directional selection goes from one extreme to the other. Reference the evolution of the peppered moth during the Industrial Age as an example.

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.