Aspecies of moth has evolved a very long tongue to reach nectar at the bottom of a species of orchid. this orchid has evolved a long nectar tube, so that moths feeding on its nectar contact its pollen, it to reproduce. this is an example of:

Coevolution

Explanation:

Coevolution is a  process in which two species evolve together because they exert selective pressures mutually. This means that one of the species changes genetically in response to a genetic change in another species. Thus, both species reciprocally affect each other's evolution. These genetic changes, which go hand in hand, are reflected in the phenotypes, that is, in the morphological traits of the species.

The coevolution of  plants (i.e the orchid)  and pollinators (i.e the moth) is a typical example of coevolution. The flowering plant adapt to a pollinator, which  in turn adapts to the plant. In this case, the nectar tube and the tongue of the moth coevolved together and the two species benefit from that. The orchid  guarantees the dispersion of its pollen while the moth guarantees its food.

as resources become scarce because of population growth, the growth decreases after few years due to lack of resources and food.

b. the carbon cycle ensures living things have a source of hydrogen