A ringing electric bell is placed inside a glass bell-jar connected to a vacuum pump. As the air is gradually removed from the jar, what will a student standing outside observe?
(a) The sound becomes louder because there is less air to absorb it.
(b) The sound becomes fainter and finally vanishes, although the bell keeps vibrating.
(c) The pitch of the sound keeps increasing while loudness remains the same.
(d) There is no change; the bell sounds equally loud throughout.