The two lowest notes on the piano are A0 (27.5 Hz) and A#0 ... ...

  The two lowest notes on the piano are A0 (27.5 Hz) and A#0 (29.1 Hz). If you play the notes simultaneously, the resulting sound seems to turn off and on and off and on. How much time exists between the successive "on"s?
(A) 0.6 s
(B) ...
(C) ...
(D) ...
(E) ...

*This question is included in 12. Sound