20 Which of these statements describes control by negative feedback? A An injury to body tissue activates platelets in the blood and these activated platelets release chemicals which activate more platelets. B During the menstrual cycle, luteinising hormone (LH) stimulates the release of oestrogen which in turn stimulates the release of more LH. C A higher concentration of carbon dioxide in the atmosphere increases temperature, which increases photosynthesis producing more carbon dioxide. D When blood pressure is high, nerve impulses from the brain cause the blood vessels to dilate and blood pressure is reduced.