Passage: Shortly after their formation in April 1985, the Parents Music Resource Center (PMRC) assembled a list of fifteen songs with deemed unsuitable content. Particular criticism was placed on "Darling Nikki" by Prince, after the daughter of PMRC co-founder Mary "Tipper" Gore recognized its references to masturbation. The Recording Industry Association of America (RIAA) responded by introducing an early version of their content warning label, although the PMRC was displeased and proposed that a music rating system structured like the Motion Picture Association of America film rating system be enacted. The RIAA alternatively suggested using a warning label reading "Parental Guidance: Explicit Lyrics", and after continued conflict between the organizations, the matter was discussed on September 19 during a hearing with the United States Senate Committee on Commerce, Science, and Transportation. Notable musicians, Frank Zappa, Dee Snider, and John Denver each testified at this hearing with strong opposition to PMRC’s warning label system, and censorship in general. Approximately two months after the hearing, the organizations agreed on a settlement in which audio recordings were to either be affixed with a warning label reading "Explicit Lyrics: Parental Advisory" or have its lyrics attached on the backside of its packaging.In 1990, the now standard black-and-white warning label design reading "Parental Advisory: Explicit Lyrics" was introduced and was to be placed on the bottom right-hand section of a given product. The first album to bear the "black and white" Parental Advisory label was the 1990 release of Banned in the U.S.A. by the rap group 2 Live Crew. By May 1992, approximately 225 records had been marked with the warning. In response to later hearings in the following years, it was reworded as "Parental Advisory: Explicit Content" in 1996. The system went unchanged until 2002, when record labels affiliated with Bertelsmann Music Group began including specific areas of concern including "strong language",...

Question: What type of job did Frank Zappa have?
musicians