Which of these scenarios is an example of natural selection?

A. Farmers crossbreed two types of cows to produce a breed of cow that has high quality beef and can tolerate a hot climate.
B. Dogs of the same breed having a desirable coat color are bred with one another to produce more puppies with that same color.
C. Giraffes with longer necks survive the dry season by eating leaves from the tops of trees. Those giraffes breed more successfully that year.
D. People capture yellow fish from the pond and breed only the most attractive individuals. This eventually results in fancy pet goldfish.