What is the relevant similarity in the following argument? "If a single cell, under appropriate conditions, becomes a person in the space of a few years, there can surely be no difficulty in understanding how, under appropriate conditions, a cell may, in the course of untold millions of years, give origin to the human race"

a.
The human race is composed of many humans in the same way a human is composed of many cells

b.
understanding human biology is difficult and understanding the existence of the human race is difficult

c.
both involve biological processes of great complexity taking place under “appropriate conditions” and commencing with a single cell

d.
a person starts from a single cell and an animal life starts from a single cell