Sound waves cannot be polarized because
A. They vibrate perpendicular to their direction of propagation
B. They vibrate along their direction of propagation
C, Their density is too low
D. Their velocity is too low

Hint: Waves are categorized into different forms on the basis of the direction of vibrations inside them. The direction of oscillations can either be parallel or perpendicular to the direction of propagation of the wave. On the basis of the direction of vibrations, we decide whether a wave can be polarized or not.

Complete step by step answer:
Wave is described as a propagating dynamic disturbance having one or more quantities associated with it. A wave involves transport of energy without transport of any kind of matter. In other words, a wave is a disturbance that propagates through a medium, transporting energy from one location to another location without transporting matter or particles.
Different types of wave include, Transverse and Longitudinal waves.
 In a transverse wave, the particles are displaced in a direction perpendicular to the direction of propagation of the wave. Example of a transverse wave is the vibrations on a string and ripples on the water surface.

In a longitudinal wave, the particles are displaced in a direction parallel to the direction of propagation of the wave. Example of a longitudinal wave is the compressions moving along a slinky.

Polarization of waves is a process that specifies the geometrical orientation of the oscillations. A wave which is vibrating in more than one plane is referred to as an Unpolarized wave. Polarized wave is one in which vibrations occur in a single plane. The process of transforming an unpolarized wave to a polarized wave is known as Polarization.
Only transverse waves can be polarized. Longitudinal waves cannot be polarized. The reason behind this is that the transverse waves can vibrate in all directions perpendicular to the direction of propagation. It is therefore feasible to continue the vibration to a single plane. On the other hand, longitudinal waves have vibrations along a single line only, and it is therefore not feasible to confine them to a plane.
Since sound waves are longitudinal waves, it is not possible to polarize them because the vibrations in sound waves are in a direction parallel to the propagation of waves.

Hence, the correct option is B.

Note: Longitudinal waves cannot be polarized because their particles vibrate in the same direction that the wave travels. A polarizer forces the transverse wave which emerges from it to be vibrating only in one plane. Longitudinal waves transfer energy by pushing neighbors in the same direction that the energy moves.