Genetic variations are the raw material for evolution. natural selection cannot act upon these variations unless which factor is present? a. the genetic variations produce only unfavorable characteristics b. the genetic variations produce only favorable characteristics c. the genetic variations are found in fossil records of the population d. the genetic variations are in the phenotype of the organism

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.

answer: substrate concentration. enzymes work best when there is a high enough substrate concentration for the reaction they catalyse.