Water coming out of the mouth of a tap and falling vertically in streamline flow forms a tapering column,i.e.,the area of cross-section of the liquid column decreases as it moves down. Which of the following is the most accurate explanation for this?

• A
  As the water moves down,its speed increases and hence its pressure decreases. It is then compressed by the atmosphere.
• B
  Falling water tries to reach a terminal velocity and hence reduces the area of cross-section to balance upward and downward forces.
• C
  The mass of water flowing past any cross-section must remain constant. Also,water is almost incompressible. Hence,the rate of volume flow must remain constant. As this is equal to velocity $\times$ area,the area decreases as velocity increases.
• D
  The surface tension causes the exposed surface area of the liquid to decrease continuously.