9. The superposition of two waves
and
at the location x = 0 in space results in
(A) Beats at a beat frequency of 6 Hz in a 153 Hz tone.
(B) A tone at a frequency of 156 Hz, as well as beats at a beat frequency of 6 Hz in a 153 Hz tone.
(C) Beats at a beat frequency of 3 Hz.
(D) A pure tone at a frequency of 153 Hz.
(E) A pure tone at a frequency of 156 Hz.