Number a is a correct one
Diffraction means spreading out of waves that has the same wavelength as the size of the gap. Sound waves have high wavelength and so it diffracts\spreads out and enables anyone to hear your voice from anywhere outside the room.
For inside the room, the sound waves doesn't actually diffract. They collide with the air particles, causing a series of compressions and rarefactions which spreads out in the air particles and anyone can hear your voice.
Air is the medium for the sound waves to travel.
D) all of the above is the answer
The answer is the diameter of the cam shaft.
This is used to compute for the area of the circle so you can multiply it with the rocker ratio to get maximum amount of weight the valve can lift.
