Which of the following statements characterizing types of waves are true?

(a) mechanical waves require a medium through which to propagate.
(b) mechanical waves can be either longitudinal, transverse, or some combination of the two
(c) the displacement of particles in a transverse wave is along the axis of the wave propagation.
(d) wavelength is used to characterize transverse waves, but not longitudinal waves

a and b.

Explanation:

In general  types of wave

1. Transverse wave  :

    In these waves particle are vibrate perpendicular to motion of waves.

 Ex : Electromagnetic wave , Radio wave .

2. Longitudinal wave :

   In these waves particle are vibrate along the motion of waves.

 Ex : Sound wave

Mechanical wave  :

1 .These are transverse wave or Longitudinal wave or combination of them .

2.These waves required medium for propagation.

3. The particle are vibrate perpendicular to motion of waves.

So the option a and b are correct.

b would be the answer

a straight line sloped