Task: Question Generation
Input (English): Passage: Lennon played a mouth organ during a bus journey to visit his cousin in Scotland; the music caught the driver's ear. Impressed, the driver told Lennon that he could have a harmonica if he came to Edinburgh the following day; the harmonica had been stored in the Edinburgh bus depot after a passenger had inadvertently left it on a bus. The professional instrument quickly replaced Lennon's toy. He would continue to play the harmonica, often using the instrument during the Beatles' Hamburg years, and it became a signature sound in the group's early recordings. His mother taught him how to play the banjo, later buying him an acoustic guitar. At 16, he played rhythm guitar with the Quarrymen.As his career progressed, he played a variety of electric guitars, predominantly the Rickenbacker 325, Epiphone Casino and Gibson J-160E, and, from the start of his solo career, the Gibson Les Paul Junior. Double Fantasy producer Jack Douglas claimed that since his Beatle days Lennon habitually tuned his D-string slightly flat, so his Aunt Mimi could tell which guitar was his on recordings. Occasionally he played a six-string bass guitar, the Fender Bass VI, providing bass on some Beatles numbers ("Back in the U.S.S.R.", "The Long and Winding Road", "Helter Skelter") that occupied McCartney with another instrument. His other instrument of choice was the piano, on which he composed many songs, including "Imagine", described as his best-known solo work. His jamming on a piano with McCartney in 1963 led to the creation of the Beatles' first US number one, "I Want to Hold Your Hand". In 1964, he became one of the first British musicians to acquire a Mellotron keyboard, though it was not heard on a Beatles recording until "Strawberry Fields Forever" in 1967.
Output (English): What was the name of the instrument acquired by Lennon was not heard on a Beatles recording until Strawberry Fields Forever?