Option 2 is the only option that makes sense. It is asking about what the nervous system (the brain) sent to the circulatory system (blood vessels). The legs would need more blood flow in order to keep the leg muscles oxygenated.
Option 1 is incorrect because if there is less blood flow to the legs, the muscles would tense up and you would not be able to run.
Option 3 is incorrect because it says the heart sends signals to the brain, which is not what the question was asking.
Option 4 is incorrect because the heart would start beating faster as your run a marathon in order to keep the body properly oxygenated.
