What is the correct classification for smooth muscle cells

Ineed to know why d is the correct answer asap

Veins have a much lower blood pressure than arteries. which of these prevents backflow of blood in veins? a. pressure applied by the heart b. one–way valves in veins c. thin muscular walls of veins

Abiology teacher asks students to give examples of genetic variations that support the idea that changes in a population’s environment affect genetic variation. which is the least supportive example? a. changes in genetics in human populationsb. antibiotic resistance in bacteria populationsc. pesticide resistance in garden insectsd. changes in the color of the peppered moth population in england