Among the following statements,the correct statement for a wave is

Water waves are

Explain the types of waves based on the direction of oscillations of the particles of the medium.

What will be the shape of a wave propagating on the sea when observed from the sea shore? Why?

Given below are some examples of wave motion. State in each case if the wave motion is transverse,longitudinal or a combination of both:
$(a)$ Motion of a kink in a longitudinal spring produced by displacing one end of the spring sideways.
$(b)$ Waves produced in a cylinder containing a liquid by moving its piston back and forth.
$(c)$ Waves produced by a motorboat sailing in water.
$(d)$ Ultrasonic waves in air produced by a vibrating quartz crystal.

In a stretched string,which type of waves can exist?