A microphone of cross-sectional area cm² is placed in front of a guitar amp./speaker emitting 16 W of sound output. If the distance between the microphone and the speaker is 2.0 cm, the energy falling on the microphone in 4.0 s is:

(A) 1 J
(B) 1 mJ
(C) 4 J
(D) 0.25 J