A vibrating body:
$\left( a \right)$ Will always produce sound.
$\left( b \right)$ May or may not produce sound if the amplitude of vibration is low.
$\left( c \right)$ Will produce a sound which is audible to humans.
$\left( d \right)$ None of the above

Hint : As we know that the object or the body which vibrates will always create a sound. And we also know that if the vibrations are large enough and if it is in the range of human frequency then we also can feel that vibration. So by using all these points we may come to the point to answer this.

Complete Step By Step Solution Any item that vibrates will make a sound. On the off chance that the amplitudes of the vibrations are sufficiently enormous and if the characteristic frequency is inside the human frequency range, at that point the vibrating article will create sound waves that are discernible. That is we can say that the sound will be audible in that situation. From this, we can conclude that it will always produce the sound.

Therefore, the option $\left( a \right)$will be the right option in this context.

Additional information
The air particles vibrate as the sound travels through the air. When the sound wave arrives at it the eardrum gets vibrated. At the point when sound waves travel through the air, each air particle vibrates to and fro, hitting the air atom close to it, which at that point additionally vibrates to and fro. The individual air atoms don't "travel" with the wave. They simply vibrate to and fro.

Note
 Sound is produced when something vibrates. The vibrating body causes the medium (water, air, and so on) around it to vibrate. Model vibrations in the air are called voyaging longitudinal waves. They are made by the vibration of an item. The vibrating air at that point makes the human eardrum vibrate which the cerebrum deciphers as sound.