Answer:
Lowering the humidity of the air.
Explanation:
The mathematical formula for the speed of sound wave is given by :
[tex]v=\sqrt{\dfrac{\gamma RT}{M}}[/tex]
Where
[tex]\gamma[/tex] is the adiabatic constant
T is the temperature of air
M is the molecular mass of the gas
or
[tex]v=\sqrt{\dfrac{B}{\rho}}[/tex]
B is the bulk modulus
[tex]\rho[/tex] is the density of the air
As the humidity of the air increases, then the number of water molecules increase. As a result, molar mass decreases and ultimately the speed of sound increases and vice versa.
So, the correct option is (A) " lowering the humidity of the air ". Hence, this is the required solution.