Question: Who is an English singer and songwriter, who has been the leader, singer and most active songwriter of Strawbs since 1967, Terry Kath or Dave Cousins ?

full_context: Document 1: Simon Cousins: Simon Cousins (born Simon Frederick Cousins, 17 January 1965, Bath, Somerset) is an English singer-songwriter and musician, who was a member of Liverpool indie country rock band The Onset and folk rockers Ophiuchus. He studied music at the Liverpool Music College and has a degree in philosophy from Liverpool University. His solo work is in an acoustic, folk / country genre, described by Tim Peacock of Whisperin and Hollerin' online magazine as "showcasing a fluid finger-picking style and a gentle, unobtrusive voice which nonetheless carries a determined presence." Seph Ong of Glasswerk National stated that Cousins' songs were "derived from real life experience" and that as a performer he "presents a series of tales that gradually unravel to build a story of the mystery of life." Cousins performed at the Glastonbury Festival, Pilton, UK in 2010, 2011 and 2016.
Document 2: Chicago 18: Chicago 18 is the fifteenth studio album by the American band Chicago, released on September 29, 1986. As the successor to 1984's multiplatinum hit "Chicago 17", this album is the first without cofounding member Peter Cetera. This is also the first album to feature Jason Scheff on bass guitar and vocals.
Document 3: Charlie Christian: Charles Henry Christian (July 29, 1916 – March 2, 1942) was an American swing and jazz guitarist.
Document 4: Dave Peverett: David Jack Peverett (16 April 1943 – 7 February 2000), also known as Lonesome Dave, was an English singer and musician, best known as the original lead vocalist and rhythm guitarist of the rock band Foghat, which he founded following his tenure in Savoy Brown.
Document 5: Peter Cetera: Peter Paul Cetera ( ; born September 13, 1944) is an American singer, songwriter, and bassist best known for being an original member of the rock band Chicago (1967–1985), before launching a successful solo career. His career as a recording artist encompasses seventeen albums with Chicago and eight solo albums.
Document 6: Dave Gahan: David "Dave" Gahan ( ; born David Callcott; 9 May 1962) is an English singer-songwriter, best known as the baritone lead singer of the electronic band Depeche Mode since their debut in 1980. He is also an accomplished solo artist, releasing albums in 2003 ("Paper Monsters") and 2007 ("Hourglass").
Document 7: Chicago 13: Chicago 13 is the eleventh studio album by the American band Chicago, released in 1979. The follow-up to "Hot Streets", "Chicago 13" is often critically disfavored. This would be the band's final release that features lead guitarist Donnie Dacus, who had followed late, founding lead guitarist, Terry Kath. All band members would contribute to the songwriting (one of only two albums where this is the case, with the other being "Chicago VII").
Document 8: Justin Hayward: Justin David Hayward (born 14 October 1946) is an English musician, best known as songwriter, lead singer, and guitarist in the rock band the Moody Blues.
Document 9: Charles Chalmers: Charles Chalmers is a saxophonist, session musician, backup singer, songwriter and producer. He has written several hit songs for many recording artists, and has also arranged & performed on many grammy winning recordings. Seven of those recordings are in the Grammy Hall of Fame : Al Green's "Let's Stay together"; Aretha Franklin's "Respect," "Chain of Fools" & "Natural Woman"; Dusty Springfield's "Son of a Preacher Man"; and Wilson Pickett's "Mustang Sally" and "Land of a Thousand Dances." He also holds an Album of the Century award for his work on Aretha Franklin's, "I Ain't Never Loved a Man the Way that I Love You."
Document 10: Tony Hooper: Tony Hooper (born 14 September 1943) is an English singer-songwriter and musician. He is best known as a founder-member of Strawbs together with Dave Cousins. He left Strawbs in 1972 after their album "Grave New World", when it became obvious that the band was moving further away from its folk roots towards rock and progressive rock. He rejoined for a 10-year stint in 1983. Hooper has been the guitarist in the Ceilidh & Barn-Dance Band Pitchfork since 1984, and is also a member of Misalliance.
Document 11: Alan Merrill: Alan Merrill (born Allan Preston Sachs; February 19, 1951) is an American vocalist, guitarist, songwriter, actor and model. In the early 1970s Merrill was the first westerner to achieve pop star status in Japan. He is the lead singer of the first ever released version and co-author of the song "I Love Rock 'n' Roll" by the Arrows in 1975.
Document 12: Dave Peacock (musician): David Victor "Dave" Peacock (born 24 May 1945) is an English musician and bass guitarist. He was raised in Ponders End and the Freezywater areas of Enfield. Peacock is best known as having been one half of the English musical duo, Chas & Dave from 1975.
Document 13: Terry Kath: Terry Alan Kath (January 31, 1946 – January 23, 1978) was an American musician and songwriter, best known as the original guitarist, one of the lead singers and founding members of the rock band Chicago. He has been praised by the band for his guitar skills and Ray Charles-influenced vocal style.
Document 14: Terry Date: Terry Date (born January 31, 1956) is an American record producer and engineer, specializing in the rock genres, especially heavy metal. He is well known for his work with Overkill, Metal Church, Slipknot, Pantera, Soulfly, White Zombie, Deftones, Dark Angel, Dream Theater, Slayer, Soundgarden and Limp Bizkit.
Document 15: Dave Cousins: Dave Cousins (born David Joseph Hindson, 7 January 1945, Hounslow, Middlesex, England) is an English singer and songwriter, who has been the leader, singer and most active songwriter of Strawbs since 1967.
ground_truth: Dave Cousins