71.
The velocity of sound is more in

72.
Echo is heard due to

73.
A person standing on a railway platform listens to the whistles of arriving and departing trains. The whistle heard is

74.
The sound produced by a bat is–

75.
Sound is heard over longer distances on rainy days because

76.
Which phenomenon is responsible for the echo of sound wave?

77.
Loudness of sound depends on

79.
The instrument which uses sound waves to measure the depth of oceans is