Given the following context:

Cleveland is directly served by 31 AM and FM radio stations, 22 of which are licensed to the city.  Commercial FM music stations are frequently the highest rated stations in the market: WAKS (contemporary hit radio), WDOK (adult contemporary), WENZ (mainstream urban), WHLK (adult hits), WGAR-FM (country), WMJI (classic hits), WMMS (active rock/hot talk), WNCX (classic rock), WQAL (hot adult contemporary), and WZAK (urban adult contemporary).  WCPN public radio functions as the local NPR affiliate, and sister station WCLV airs a classical music format.  College radio stations include WBWC (Baldwin Wallace University), WCSB (Cleveland State University), WJCU (John Carroll University), and WRUW-FM (Case Western Reserve University).
News/talk station WTAM serves as the AM flagship for both the Cleveland Cavaliers and Cleveland Indians.  WKNR and WWGK cover sports via ESPN Radio, while WKRK-FM covers sports via CBS Sports Radio (WKNR and WKRK-FM are also co-flagship stations for the Cleveland Browns). As WJW (AM), WKNR was once the home of Alan Freed − the Cleveland disc jockey credited with first using and popularizing the term "rock and roll" to describe the music genre.  News/talk station WHK was one of the first radio stations to broadcast in the United States and the first in Ohio; its former sister station, rock station WMMS, dominated Cleveland radio in the 1970s and 1980s and was at that time one of the highest rated radio stations in the country.  In 1972, WMMS program director Billy Bass coined the phrase "The Rock and Roll Capital of the World" to describe Cleveland.  In 1987, Playboy named WMMS DJ Kid Leo (Lawrence Travagliante) "The Best Disc Jockey in the Country".

answer the following question:

Whose former sister station dominated Cleveland radio in the 1970s and 1980s? 

WHK