When a glacier retreats, it leaves barren rock, no soil or plants. What is this an example of?A. Primary successionB. Secondary successionC. BothD. re-introduction

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.