Which of the following statement is wrong?

• The critical pressure gives the velocity of steam at the throat equal to the velocity of sound.
• The flowin the convergent portion of the nozzle is sub-sonic.
• The flow in the divergent portion of the nozzle is super-sonic.
• To increase the velocity of steam above sonic velocity (super-sonic) by expanding steam below the critical pressure, the divergent portion for the nozzle is not necessary.