Fill in the blanks with suitable words:

(a) Sound is caused by ………..

(b) A sound wave consists of places of higher pressure called ………. and places of ……….. pressure called ………..

(c) Wave speed in meters per second equals frequency in ……… multiplied by ……….. in ………..

(d) Sound cannot travel through …………

(e) The speed of sound in a solid is ……… than the speed of sound in air.

(f) When the frequency of the sound is increased, the wavelength ……..