Correct Answer : Option (C) :   u – a

Explaination : At a point (x,y) in an x – y plane there exists paths through this point known as C₊ and C_– characteristic lines. They represent the path of sound waves which are left and right running. The slope for a C_– characteristic line is given by u – a and for C₊ characteristic is u + a.

Correct Answer : Option (D) :   Compression region

Explanation : The density of the finite wave varies along the distance of its propagation. The region where the density increases is known as the finite compression region, and the portion where the density decreases is known as the finite expansion region.

Correct Answer : Option (B) :   Linear equations are used to govern the flow variables

Explanation : Finite waves unlike the sound waves have high perturbation of density, velocity, temperature etc. They are known to propagate at speed which is an addition of local speed of mass velocity and speed of sound. The shape of the finite wave does not remain constant like the sound waves and the flow variables are governed by the nonlinear equations.