What does the measurement 45 N represent in the photograph?

the answer is c.) there is a warm front in region a and a stationary front in region b.

i think the answer is b.

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.