Two capillary tubes of same radius `r` but of lengths `l_(1)` and `l_(2)` are fitted in parallel to the bottom of a vessel. The pressure to the bottom of a vessel. The pressure head is P. What should be the length of a single tube of same radius that can replace the two tubes so that the rate of flow is same as before?
A. `l_(1) + l_(2)`
B. `(1)/(l_(1)) + (1)/(l_(2))`
C. `(l_(1)l_(2))/(l_(1) + l_(2))`
D. `(1)/(l_(1) + l_(2))`
