Blood pressure decreases from arteries to veins Steps:

• Blood exits the heart into arteries at high pressure (systolic ~120 mmHg).
• Pressure drops sharply in arterioles and capillaries due to friction and resistance.
• In veins, pressure remains low (~0-10 mmHg) as blood flows back to the heart aided by valves and muscle pumps.
• The diagram line for veins shows this minimal, steady low pressure.

Why D is correct:

• D illustrates low venous pressure, defined as near-atmospheric levels post-capillary resistance per Poiseuille's law on flow resistance.

Why the others are wrong:

• A: Depicts high arterial pressure peaks, not venous return.
• B: Shows intermediate capillary drop, higher than veins.
• C: Represents arterial or arteriolar fluctuations, not low venous steady state.

Final answer: D