Which sentence describes the action of natural selection? 1. ) an ecosystem contains two types of giraffes, some with short necks and others with long necks. 2.) the distribution of this trait is equal among the population. 3.) a disease causes low-lying shrubs to die out. 4.) the long-necked giraffes can access more food, so they have a better chance of surviving to reproductive age.

4.) The long-necked giraffes can access more food, so they have a better chance of surviving to reproductive age.

Explanation:

Natural selection can be define as the differential survival and reproduction of individuals in the population of the species which exhibit better phenotypic traits over the others.

Among the options given, 4.) The long-necked giraffes can access more food, so they have a better chance of surviving to reproductive age. is the correct one because of the fact that long neck is the phenotypic trait which avails the giraffe to fetch food. The giraffe population has obtained this trait through evolution as due to lack of food at the ground level. Some individuals in the giraffe population extended their necks to reach upto the tree tops so as to obtain the leaves. This trait passed on to the next generation through sexual reproduction and proved to be a beneficiary trait in the scarcity of food.  

it creates acid rain

genetic variation can be caused by mutation (which can create entirely new alleles in a population), random mating, random fertilization, and recombination between homologous chromosomes during meiosis (which reshuffles alleles within an organism's offspring).