Water falling vertically from the mouth of a tap in streamline flow forms a tapering column as shown in the Fig. 12.69. Which of the following is the most correct explanation for this?
 

• A

  As the water falls down, its velocity increases resulting in decrease in pressure. So, it is then compressed by the surrounding air.

• B

  The mass of water passing through any cross-section must remain constant. So in accordance with Av = constant (as liquid is incompressible), the area of cross-section decreases with increase in velocity.

• C

  Due to surface tension effect, exposed surface area of liquid decreases.

• D

  To attain terminal velocity, area of cross-section decreases.