Why are most systems in the human body negative feedback systems?

Round seeds and yellow seed color are dominant to wrinkled seeds and green seed color. which punnett square represents the correct way to set up the cross rryy  ´  rryy? 

Moving down the ramp from 6 meters to

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