Answers to my questions（6）

12  Are there any groups that support/ against music censorship?
 There is a NGO that advocates for the rights of musicians all around the world. Recently they advocated that  3 March every year should be MUSIC FREEDOM DAY since 2013. Here is their official site  http://www.freemuse.org/sw305.asp
 And the most famous organisation that support music censorship is PMRC, which I mentioned many times before.
 However I was surprised that I can't find the official site of PMRC. It seems that they don't have a site. so here is their information from wiki

 "Parents Music Resource Center." wikipedia. Print. <http://en.wikipedia.org/wiki/Parents_Music_Resource_Center>.

13 Are there any different between music censorship in1970s,1980s,1990s and now? Is is becoming more and more serious?
 In 1970s the real music censorship haven't started yet, so there wasn't a standard about which music should be censored and which shouldn't.
 In 1980s when the PMRC was found, the music censorship became more serious , at that time, PMRC mainly against heavy metal music because according to some parents some teenagers try to kill themselves after listening to the heavy metal music ( like  Ozzy's case and Judas Priest's case )
 In 1980s when Hip HOP and Rap rise, they became the main object of PMRC.

Here is the Timeline of Music censorship

"History of Censorship in America." n. page. Print. <http://www.nku.edu/~issues/music_censorship/History.htm>.