Which of the Following Is an Example of "Natural Selection

Which of the following is an example of "natural selection"?

A) humming birds with beaks that, through mutation, happen to be ideal for dipping into the flowers found in their habitat
B) coyotes rummaging among the ruins of ghost towns for items useful in lair building
C) the birds that live on the rhinos
D) the fishes that take up residence in the depths of the ocean in natural caves, relative to their cousins that attempt to survive in the open at shallow levels