a) Change of flow equations from elliptic to hyperbolic
b) High speed with high temperature
c) Supersonic Mach number
d) High temperatures

Answer: a
Explanation: Straight to the nose of the vehicle, the shock is normal. This results in a subsonic region and elliptic flow equations. But, downstream the shock is oblique which creates a supersonic region resulting in the elliptic equation. This was the problem in modelling supersonic blunt nose. In later years this was overcome by a better model.