Blood pressure is generated byA. Valves in the heart B. Contractions of the heart muscle C. Veins D. Contractions of the diaphragm muscle

The answer is B, contractions of the heart muscle.

Explanation:

Basically blood pressure is the pressure in which your blood is pushed away from the heart to the other parts of your body.  So the force in which the heart has to use to pump that blood is the blood pressure.  This is called the systolic pressure.  The harder your heart has to work to pump the blood, the higher your pressure will be.  There's a secondary pressure is called diastolic pressure.  This is the second force where your heart rests between pumps.  So you will have 2 numbers for blood pressure, the systolic and the diastolic.  You want your heart to work as little as possible to pump the blood through your body.

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.