Consider the following statements:

Statement I: When a particle is executing simple harmonic motion, total energy varies with time.

Statement II: Audible waves have a frequency range of $30$ kHz to $30$ MHz.

Which of the above statement (s) is/are correct?

Consider the following statements:

Statement I: Radar waves are sent towards a moving aeroplane and the reflected waves are received. When the aeroplane is moving towards the radar, the wavelength of the wave decreases. 

Statement II: The velocity of sound in the air decreases with increase in pressure.

Which of the above statement (s) is/are correct?

When an aeroplane attains a speed higher than the speed of sound in air, a loud band is heard this is because _____.