When it comes to blood circulation, a good and effective blood circulation is one that provides the body with a lot of nutrients - so what we want is for example an increased blood circulation to the body, but we don't want for example a decreased blood flow to some organs - those organs would then not receive the necessary nutrition. Healthy lifestyle provides good things to the body - so the answer is D, since it's the only good thing. Decreased area in blood vessels would again diminish the nutrition to some organs and a high blood pressure is also not good - it carries a risk of some diseases.