Scientists have known for decades that humans were changing the global climate, but levels continue to rise every year. Why is it difficult to reduce CO2 emissions? And what are the most promising solutions?

the answers are a and c

these muscles maintain the blood pressure in the vessels. the smooth muscles are innervated by nerves of the autonomic nervous system. when the muscles contract, they cause vasoconstriction of the vessels and increase blood pressure. when the muscles relax, they enable vasodilation of the   blood vessels hence reduce blood pressure.