A liquid is flowing in a horizontal uniform capillary tube under a constant pressure difference P. The value of pressure for which the rate of flow of the liquid is doubled when the radius and length both are doubled is [EAMCET 2001]

• A.            P    
• B.            \[\frac{3P}{4}\]                   
• C.            \[\frac{P}{2}\]                     
• D.            \[\frac{P}{4}\]