It would be the muscles because their contracting and forcing the blood back to the heart
The correct answer is c. Genetic Variation. Bacteria are very numerous, ad random mutation of bacterial DNA generates a wide variety of change, including resistance.
I am going with x-rays; it is the most visible to the naked eye out of all the choices.
Answer:
directional selection
Explanation:
The directional selection is a type of Darwinian selection where a particular phenotype is favored in the population, thereby modifying the allelic frequencies to increase the proportion of the favored phenotype. <em>Biston betularia</em>, also known as peppered moth, is a species that was influenced by directional selection in its recent past. Before the industrial revolution, the frequency of light-colored moths was predominant compared to the darker-colored phenotypes, because this color has higher adaptive fitness in a clean, no pollution environment, thereby light-colored moths were able to avoid predatory birds. However, during the industrial revolution, the frequency of dark-colored moths increased in response to pollution (i.e. darker environment), thereby conferring a higher adaptive fitness to darker phenotypes.
