$A$ closed pipe containing liquid showed a pressure $P_{1}$ by gauge. When the valve is opened,the pressure was reduced to $P_{2}$. The speed of water flowing out of the pipe is $[\rho = \text{density of water}]$

• A
  $\left[\frac{2(P_{1}+P_{2})}{\rho}\right]^{1/2}$
• B
  $\left[\frac{2(P_{1}-P_{2})}{\rho}\right]^{1/2}$
• C
  $\left[\frac{\rho}{2(P_{1}-P_{2})}\right]^{1/2}$
• D
  $\left[\frac{\rho}{2(P_{1}+P_{2})}\right]^{1/2}$