Consider the following statements:
Isentropic flow through a steam nozzle becomes “chocked‟ when
1. Discharge is maximum
2. Discharge is zero
3. Nozzle pressure ratio is $\leq$ critical pressure ratio
4. Throat velocity reaches sonic value
Which of these statements are correct?
(A) 1, 2, 3 and 4 (B) 1, 2 and 3 only
(C) 2, 3 and 4 only (D) 1, 3 and 4 only