If You Were to Inhale a Few Breaths from a Helium

If you were to inhale a few breaths from a helium gas balloon, you would probably experience an amusing change in your voice. You would sound like Donald Duck or Alvin the Chipmunk. What is the cause of this curious high-pitched effect?

A) Low frequencies are absorbed in helium gas, leaving the high frequency components, which result in the high, squeaky sound.
B) The helium causes your vocal cords to tighten and vibrate at a higher frequency.
C) Your voice box is resonating at the second harmonic, rather than at the fundamental frequency.
D) For a given frequency of vibration of your vocal cords, the wavelength of sound is less in helium than it is in air.
E) Sound travels faster in helium than in air at a given temperature.