Question: The Statler Brothers had their biggest country hit with "Do You Remember These" in 1972, but which famous singer did they sing backup for?
Context: "Do You Know You Are My Sunshine" is a song written by Don Reid and Harold Reid, and recorded by American country music group The Statler Brothers.  It was released in March 1978 as the first single from the album "Entertainers On and Off the Record".  "Do You Know You Are My Sunshine" was The Statler Brothers twenty-seventh country hit and the first of four number ones on the country chart, as well as the group's only number one with original tenor Lew DeWitt.  The single stayed at number one for two weeks and spent a total of eleven weeks on the country chart. Sing the Big Hits (a.k.a. "The Statler Brothers Sing the Big Hits") is the second studio album by The Statler Brothers.  It produced their hit singles "Ruthless" and "You Can't Have Your Kate and Edith, Too" which both peaked at #10 on the Billboard's Hot Country Songs chart. "Elizabeth" is a song written by Jimmy Fortune, and recorded by American country music group The Statler Brothers.  It was released in November 1983 as the second single from the album "Today".  "Elizabeth" was The Statler Brothers' forty-fourth country hit and their second number one on the country charts.  The single went to number one for one week and spent a total of thirteen weeks on the country chart. The Statler Brothers Show was an American television variety show hosted by country music group The Statler Brothers.  The show ran for seven seasons from 1991 to 1998 on The Nashville Network (TNN) as part of the network's Saturday night lineup and became the most popular show on TNN, including being the highest rated show in the network's history.  The show's theme music is an instrumental of "The Class of '57," one of the Statlers' biggest hits as performed by the Bill Walker Orchestra, which along with the Statlers' band, provided all the music for the show. The discography of The Statler Brothers, an American country music group, consists of 38 albums and 69 singles.  The group debuted in 1965 with "Flowers on the Wall", a number 2 country and number 4 pop hit.  Although they never made top 40 on the pop charts again, The Statler Brothers continued to chart on Hot Country Songs until 1990, reaching number one with "Do You Know You Are My Sunshine" in 1978; "Elizabeth" in 1984; and "My Only Love" and "Too Much on My Heart," both in 1985. "Do You Remember These" is a song written by Don Reid, Harold Reid and Larry Lee, and recorded by American country music group The Statler Brothers.  It was released in March 1972 as the first single from the album "Innerview".  The song reached no. 2 on the "Billboard" Hot Country Singles & Tracks chart.  "Do You Remember These" was also The Statler Brothers sole entry on the Easy Listening chart, where it peaked at no. 18. "I'll Go to My Grave Loving You" is a song written by Don Reid, and recorded by American country music group The Statler Brothers.  It was released in May 1975 as the first single from their album "The Best of the Statler Brothers".  The song peaked at number 3 on the "Billboard" Hot Country Singles chart.  It also reached number 1 on the "RPM" Country Tracks chart in Canada.  It is based upon a song by Harold Reid, another member of the group, called "He Went to the Cross Loving You". "Too Much on My Heart" is a song written by Jimmy Fortune, and recorded by American country music group The Statler Brothers.  It was released in July 1985 as the second single from the album "Pardners in Rhyme".  "Too Much on My Heart" was The Statler Brothers' last of four number ones on the country chart.  The single stayed at number one for one week and spent a total of fourteen weeks on the country chart. The Statler Brothers (sometimes referred to in country music circles as simply The Statlers) were an American country music, gospel, and vocal group.  The quartet was formed in 1955 performing locally and, in 1964, they began singing backup for Johnny Cash. "The Class of '57" is a song written by Don Reid and Harold Reid, and recorded by American country music group The Statler Brothers.  It was released in August 1972 as the first single from the album "Country Music Then and Now".  The song reached #6 on the "Billboard" Hot Country Singles & Tracks chart.  The song was also critically acclaimed with the Statler Brothers winning the 1972 Grammy Award for Best Country Vocal Performance by a Duo or Group.
Answer: Johnny Cash