During an Apollo-era demonstration on the lunar surface, an astronaut struck two metal hammers together while a nearby camera simultaneously transmitted video and audio signals to Earth. Viewers saw the collision but heard no sound from it. Which of the following best explains why the video signal was received but the sound was not?
(a) Because sound travels far slower than light, the hammer’s sound had not yet reached Earth when the video signal arrived.
(b) The vacuum surrounding the Moon prevents mechanical sound waves from propagating, whereas electromagnetic television signals can travel through space.
(c) Sound intensity obeys an inverse-square law, so over the Moon-to-Earth distance it became too faint to detect, while the radio signal remained strong.
(d) The Moon’s weak gravity changes the pitch of the sound, shifting it outside the audible range, but it does not affect radio waves.