$A$ pipe having an internal diameter $D$ is connected to another pipe of the same size. Water flows into the second pipe through $n$ holes,each of diameter $d$. If the water in the first pipe has speed $v$,the speed of water leaving the second pipe is

• A
  $\frac{D^2 v}{n d^2}$
• B
  $\frac{D^2 v}{d^2}$
• C
  $\frac{n d^2 v}{D^2}$
• D
  $\frac{d^2 v}{D^2}$