The Noise- Reduction Coefficient (NRC)of a Material Is Evaluated Between

The noise- reduction coefficient (NRC) of a material is evaluated between the frequency range of 250 Hz and 2 kHz because

A) most of the sound energy in the noise produced in buildings lies in the given frequency range.
B) most of the sound energy in human speech lies in the given frequency range.
C) the human ear is insensitive to noise outside the above frequency range.
D) it is virtually impossible to evaluate this property outside the above frequency range.
E) none of the above.