Beta-adrenergic blocking agents decrease the oxygen demands of the heart by what mechanism? A. Increasing cardiac output, thereby increasing the oxygen supplied to the heartB. Increasing blood pressure, which increases the amount of blood returned to the heartC. Increasing conduction to the atrioventricular node, thereby increasing cardiac outputD. Decreasing the heart rate, allowing for longer filling time and increased blood to the heart

option D

Explanation:

beta blockers usually decreases the blood pressure by inhibiting the release of adrenaline also known as epinephrine hormone which have sympathetic effects on heart. Beta blockers works by slowing down the heart rate, so less oxygen is needed by heart to pump the blood and takes longer time in filling.

but beta blockers are not recommended in hypertension. and they are also not used in asthmatic patient as it can worsen the asthma.