Consider the following statements:
1. The cause of stalling of an aerofoil is the boundary layer separation and formation of increased zone of wake.
2. An aerofoil should have a rounded nose in supersonic flow to prevent formation of new shock.
3. When an aerofoil operates at an angle of incidence greater than that of stalling, the lift decreases and drag increases.
4. A rough ball when at certain speeds can attain longer range due to reduction of lift as the roughness induces early separation?
Which of these statements are correct?
(a) 3 and 4 (b) 1 and 2
(c) 2 and 4 (d) 1 and 3