What is meant by natural selection?

Explanation:

Natural selection is process of differential survival and reproduction of the organisms which have better phenotypic traits over the other members of the same species. These traits help the organism to survive in unfavorable conditions and they are passed from the parents to the offsprings and through successive generations of the species.

For example, the development of long neck of the giraffe helped them to grab leaves from tree tops.

answer; i believe the correct answer to the above question is ( friction)

when you breathe in, or inhale, your diaphragm contracts (tightens) and moves downward. this increases the space in your chest cavity, into which your lungs expand. the intercostal muscles between your ribs also enlarge the chest cavity. they contract to pull your rib cage both upward and outward when you inhale.