Compact Disc (CD) is a digital optical disc data storage format. The format was originally developed to store and play only sound recordings but was later adapted for storage of data (CD-ROM). Several other formats were further derived from these, including write-once audio and data storage (CD-R), rewritable media (CD-RW), Video Compact Disc (VCD), Super Video Compact Disc (SVCD), Photo CD, PictureCD, CD-i, and Enhanced Music CD. Audio CDs and audio CD players have been commercially available since October 1982. 

In 2004, worldwide sales of audio CDs, CD-ROMs and CD-Rs reached about 30 billion discs. By 2007, 200 billion CDs had been sold worldwide. CDs are increasingly being replaced by other forms of digital storage and distribution, with the result that audio CD sales rates in the U.S. have dropped about 50% from their peak; however, they remain one of the primary distribution methods for the music industry. In 2014, revenues from digital music services matched those from physical format sales for the first time.

What are the answers to this following set of questions:

1. What is a compact disc?
2. What is it's abbreviation?
3. Why was it invented?
4. Any other reasons?
5. Does that disc have a different name?
6. What?
7. Are there other formats?
8. How many?
9. Name two of these?
10. What is VCD?
11. How long have CDs been available to the public?
12. How many sales did it reach in 2004?
13. How many sold around the world by 2007?
14. Are they still as popular?
15. Why?
16. Have sales dropped?
17. By how much?
18. How were sales in 2014?
19. What does CD-RW mean?
20. Name another form?

Numbered answers:
1. digital optical disc data storage format
2. CD
3. to store and play only sound recording
4. for storage of data
5. Yes
6. CD-ROM
7. Yes
8. 10
9. CD-R and CD-RW
10. Video Compact Disc
11. since October 1982.
12. about 30 billion discs
13. 200 billion
14. No
15. being replaced by other forms of digital storage and distribution,
16. Yes
17. about 50% from their peak;
18. revenues from digital music services matched those from physical format sales for the first time.
19. rewritable media
20. Super Video Compact Disc (SVCD)