I have a test where I am given the following article, what is an answer for the question: What is the name of the band Harrison sought to alleviate tensions within, while improving their live sound, by inviting keyboardist Billy Preston to participate in the last nine days of sessions? ?

Although Let It Be was the Beatles' final album release, it was largely recorded before Abbey Road. The project's impetus came from an idea Martin attributes to McCartney, who suggested they "record an album of new material and rehearse it, then perform it before a live audience for the very first time – on record and on film". Originally intended for a one-hour television programme to be called Beatles at Work, in the event much of the album's content came from studio work beginning in January 1969, many hours of which were captured on film by director Michael Lindsay-Hogg. Martin has said that the project was "not at all a happy recording experience. It was a time when relations between the Beatles were at their lowest ebb." Lennon described the largely impromptu sessions as "hell ... the most miserable ... on Earth", and Harrison, "the low of all-time". Irritated by both McCartney and Lennon, Harrison walked out for five days. Upon returning, he threatened to leave the band unless they "abandon[ed] all talk of live performance" and instead focused on finishing a new album, initially titled Get Back, using songs recorded for the TV special. He also demanded they cease work at Twickenham Film Studios, where the sessions had begun, and relocate to the newly finished Apple Studio. The other band members agreed, and the idea came about to salvage the footage shot for the TV production for use in a feature film.
In an effort to alleviate tensions within the band and improve the quality of their live sound, Harrison invited keyboardist Billy Preston to participate in the last nine days of sessions. Preston received label billing on the "Get Back" single – the only musician ever to receive that acknowledgment on an official Beatles release. At the conclusion of the rehearsals, the band could not agree on a location to film a concert, rejecting several ideas, including a boat at sea, a lunatic asylum, the Tunisian desert, and the Colosseum. Ultimately, what would be their final live performance was filmed on the...

the Beatles