Five decibels is often added to the usual presentation level for speech recognition tests when masking is used to A. increase the interaural attenuation B. decrease the interaural attenuation C. account for cross-hearing D. offset central masking

D. Offset central masking

Explanation:

A 5 dB threshold elevation is usually created by a noise being near-threshold-levels.

If you don't mask (offsetting), the threshold will be 5 dB better and it will produce minor air-bone gaps.

Central masking can be used as a means of investigating normal and pathological auditory nervous system.