Context: The logical format of an audio CD (officially Compact Disc Digital Audio or CD-DA) is described in a document produced in 1980 by the format's joint creators, Sony and Philips. The document is known colloquially as the Red Book CD-DA after the colour of its cover. The format is a two-channel 16-bit PCM encoding at a 44.1 kHz sampling rate per channel. Four-channel sound was to be an allowable option within the Red Book format, but has never been implemented. Monaural audio has no existing standard on a Red Book CD; thus, mono source material is usually presented as two identical channels in a standard Red Book stereo track (i.e., mirrored mono); an MP3 CD, however, can have audio file formats with mono sound.

Question: Where does the Red Book get it's name from?
Answer: the colour of its cover

Question: What is the formal name for a CD? 
Answer: Compact Disc Digital Audio

Question: Do CDs have a two or four channel format?
Answer: two-channel

Question: What format has never been implemented on CDs?
Answer: Four-channel sound

Question: What was the sampling rate for the four-channel sound?
Answer: Unanswerable

Question: When was four-channel sound implemented?
Answer: Unanswerable

Question: What is the Red Book format for monaural audio?
Answer: Unanswerable

Question: What is the official name of the Red Book?
Answer: Unanswerable

Question: What is the PCM for an MP3 mono sound chanel?
Answer: Unanswerable