Task: Question Answering
Input (English): Passage: The first three symphonies, to which Vaughan Williams assigned titles rather than numbers, form a sub-group within the nine, having programmatic elements, absent from the later six.A Sea Symphony (1910), the only one of the series to include a part for full choir, differs from most earlier choral symphonies in that the choir sings in all the movements. The extent to which it is a true symphony has been debated; in a 2013 study, Alain Frogley describes it as a hybrid work, with elements of symphony, oratorio and cantata. Its sheer length—about eighty minutes—was unprecedented for an English symphonic work, and within its thoroughly tonal construction it contains harmonic dissonances that pre-echo the early works of Stravinsky which were soon to follow.A London Symphony (1911–1913) which the composer later observed might more accurately be called a "symphony by a Londoner", is for the most part not overtly pictorial in its presentation of London. Vaughan Williams insisted that it is "self-expressive, and must stand or fall as 'absolute' music". There are some references to the urban soundscape: brief impressions of street music, with the sound of the barrel organ mimicked by the orchestra; the characteristic chant of the lavender-seller; the jingle of hansom cabs; and the chimes of Big Ben played by harp and clarinet. But commentators have heard—and the composer never denied or confirmed—some social comment in sinister echoes at the end of the scherzo and an orchestral outburst of pain and despair at the opening of the finale. Schwartz comments that the symphony, in its "unified presentation of widely heterogeneous elements", is "very much like the city itself". Vaughan Williams said in his later years that this was his favourite of the symphonies.The last of the first group is A Pastoral Symphony (1921). The first three movements are for orchestra alone; a wordless solo soprano or tenor voice is added in the finale. Despite the title the symphony draws little on the folk-songs beloved of the composer, and the pastoral landscape evoked is not a tranquil English scene, but the French countryside ravaged by war. Some English musicians who had not fought in the First World War misunderstood the work and heard only the slow tempi and quiet tone, failing to notice the character of a requiem in the music and mistaking the piece for a rustic idyll. Kennedy comments that it was not until after the Second World War that "the spectral 'Last Post' in the second movement and the girl's lamenting voice in the finale" were widely noticed and understood. 
Question: What is the name of the symphony Vaughan Williams said in later years was his favorite?
Output (English): A London Symphony.