How is natural selection in the evolution of long necks in giraffes best explained?

E. None of the above. Giraffes with longer necks were presumably able to get more food with less effort and less competition, allowing them to produce more offspring than giraffes with shorter necks. The more offspring of the longer-necked giraffes carried the "longer neck" genes, which gradually spread throughout the giraffe population. That's the simple version, anyway.