Two capillary tubes of the same length but different radii r1 and r2 are fitted in parallel to the bottom of a vessel. The pressure head is P. What should be the radius of a single tube that can replace the two tubes so that the rate of flow is same as before

• A.             \[{{r}_{1}}+{{r}_{2}}\]        
• B.             \[r_{1}^{2}+r_{2}^{2}\]
• C.             \[r_{1}^{4}+r_{2}^{4}\]    
• D.             None of these