Which property distinguishes progressive waves from stationary waves?

The intensity level at a distance of $200 \ cm$ from a sound source is $80 \ dB$. If there is no loss of acoustic power in the air and the threshold intensity of hearing is $10^{-12} \ W/m^2$,what is the intensity level at a distance of $400 \ cm$ from the source (in $dB$)?

Which of the following statements is correct?

What is carried by the waves? Mass,velocity,or energy?

$A$ is singing a note and at the same time $B$ is singing a note with exactly one-eighth the frequency of the note of $A$. If the energies of the two sounds are equal,the amplitude of the note of $B$ is:

If the ratio of the amplitudes of two waves is $2:1$,then the ratio of their maximum and minimum intensity is: