Consider the following statements relating to compressible flow :
1. In a contracting conduit, sonic velocity is reached in the minimum cross-sectional area.
2.
In a contracting conduit, supersonic velocities are reached only in the
expanding section downstream from the minimum section.
3. An expansion shockwave is physically possible and can be exhibited.
4.
In the Laval nozzle it is possible to obtain a velocity greater than
the velocity of sound in the expanding section of nozzle.
Of these statements :