For Natural Selection to Occur,there Must Be Competition for Resources,competition

For natural selection to occur,there must be competition for resources,competition for survival,or different reproductive success.Why is this so?

A) The struggle of competition makes individuals stronger.
B) Populations evolve to preserve the species and don't change unless they must.
C) Without competition, there is no pressure to mutate.
D) Natural selection acts on the different abilities of individuals to survive and pass on their genes to the next generation.