Across the normal shockwave:
1. Stagnation pressure decreases whereas stagnation temperature remains constant
2. Mach number before the shock–wave is always greater than one and after the shockwave, the Mach number need not be less than one
3. Across the shockwave there is a rise in pressure and temperature
4. The product of Mach number downstream of normal shockwave and upstream of normal shockwave is always one
Which of the above statements are correct?
(A) 1 and 3 (B) 2 and 3
(C) 1 and 4 (D) 2 and 4