Read the passage below and answer the question <br><br> Sound waves are longitudinal waves, which means they vibrate in the same direction as the direction of travel. Sound waves can only travel through solids, liquids or gases. A good model of sound waves is a spring. The section of waves when they are pushed together are areas of compressions and when the particles are far apart the areas are called rarefactions. Sound waves can be reflected, refracted and diffracted.<br><br> The hearing range of Human ear is 20Hz to 20KHz. Sounds with frequencies below 20Hz are called Infrasound and sound waves with frequencies above 20KHz are called Ultra sound. These waves have a wide applications in various fields like industry, medicine, agriculture etc; Speed of the sound can be calculated by the equation speed of sound = distance / time. <br><br> QUESTION : Sound waves are longitudinal waves because

Question

$\begin{array}{1 1} (a)\;\text{the particles vibrate along the line of propagation} \\ (b)\; \text{the particles vibrate perpendicular to the line of propagation} \\ (c)\; \text{the particles need a medium to propagate} \\ (d)\; \text{none of the above} \end{array}$