The correct answer is: A. Reverberation
Reverberation is the persistence of sound after the source has ceased making the sound. It is caused by sound waves reflecting off of surfaces. The longer the reverberation time, the longer the sound will continue to be heard after the source has stopped making the sound.
Echo is a sound that is repeated because the sound waves are reflected back from a surface. The time it takes for the echo to return depends on the distance of the reflecting surface.
Intensity of sound is a measure of the amount of energy in a sound wave. It is measured in decibels (dB). The higher the decibel level, the louder the sound.
Interference is the interaction of two or more waves that results in a new wave pattern. The new wave pattern can be constructive, destructive, or neither.
In conclusion, the sound which continues even after its source is cut off is called reverberation.