Pinna
a)	Collects the vibrations in the air which produce sound
b)	Are wax secreting glands
c)	Increase the efficiency of transmission of sound waves to the inner ear
d)	All of the above

(d)

The pinna collects the vibrations in the air, which produce sound. The external auditory meatus leads inwards and extends upto the tympanic membrane (the ear drum). There are very fine hairs and wax secreting sebaceous glands in the skin of pinna and meatus. The tympanic membrane is composed of connective tissues covered with skin outside and with mucus membrane inside