Task: Question Answering
Input (English): Passage: Martin recalled that Sgt. Pepper "grew naturally out of Revolver", marking "an era of almost continuous technological experimentation". According to Geoff Emerick, the Beatles' recording engineer, the "major difference" between the two albums was that, with Sgt. Pepper, there was no absolute deadline for completion. Sessions began on 24 November 1966 in Studio Two at EMI Studios (subsequently Abbey Road Studios), marking the first time that the Beatles had come together since September. Afforded the luxury of a nearly limitless recording budget, the band booked open-ended sessions that started at 7 pm and allowed them to work as late as they wanted. They began with "Strawberry Fields Forever", followed by two other songs that were thematically linked to their childhoods: "When I'm Sixty-Four", the first session for which took place on 6 December, and "Penny Lane". "Strawberry Fields Forever" made prominent use of Mellotron, a keyboard instrument on which the keys triggered tape-recordings of a variety of instruments, enabling its user to play keyboard parts using those voices."Strawberry Fields Forever" and "Penny Lane" were subsequently released as a double A-side in February 1967 after EMI and Epstein pressured Martin for a single. When it failed to reach number one in the UK, British press agencies speculated that the group's run of success might have ended, with headlines such as "Beatles Fail to Reach the Top", "First Time in Four Years" and "Has the Bubble Burst?" In keeping with the band's approach to their previously issued singles, the songs were then excluded from Sgt. Pepper. Martin later described the decision to drop these two songs as "the biggest mistake of my professional life". In his judgment, "Strawberry Fields Forever", which he and the band spent an unprecedented 55 hours of studio time recording, "set the agenda for the whole album". He explained: "It was going to be a record ... [with songs that] couldn't be performed live: they were designed to be studio productions and that was the difference." McCartney declared: "Now our performance is that record.". 
Question: What songs did not appear on Sgt. Pepper?
Output (English): "Strawberry Fields Forever".