Natural selection is the process that result in the adaptation of an organism to environment by means of selectively reproducing changes in its genotype, or genetic constitution. It is the a key mechanism of evolution. Charles Darwin popularised the term "natural selection" contrasting it with artificial selection, which is intentional, whereas natural selection is not.
To make it simple, let's have a group of beetle composing of green and some are brown as an example. here, there is a variation in traits. Since the environment could not support continuous population growth, not all species can reproduce to their full potential. Green beetles can easily be eaten by other species like birds compared to brown beetles. The surviving brown beetles will then generate brown offsprings because their trait has a genetic basis. Since more brown beetles survive and becomes more common in the population, the process continues until all individuals will eventually be brown. so basically, if you have variation, differential reproduction, and heredity, you will have evolution by natural selection as an outcome.
I'm pretty sure it is "c"
Whales play an important role in stabilizing the aquatic food chain and reproduction of other species.
As more whales are killed the food distribution in the ocean becomes destabilized and causes changes in the food supply of many other kinds of marine life.
Whales are vital to the food chain, stabilising food flow and maintaining a healthy ocean.
As such, the rapidly decreasing whale population will have major effects on the ocean's ecosystem.
Believe it or not, whale poop also serves quite an important purpose to the ecosystem.
