Task: Question Answering
Input (English): Passage: Ravel was not by inclination a teacher, but he gave lessons to a few young musicians he felt could benefit from them. Manuel Rosenthal was one, and records that Ravel was a very demanding teacher when he thought his pupil had talent. Like his own teacher, Fauré, he was concerned that his pupils should find their own individual voices and not be excessively influenced by established masters. He warned Rosenthal that it was impossible to learn from studying Debussy's music: "Only Debussy could have written it and made it sound like only Debussy can sound." When George Gershwin asked him for lessons in the 1920s, Ravel, after serious consideration, refused, on the grounds that they "would probably cause him to write bad Ravel and lose his great gift of melody and spontaneity". The best known composer who studied with Ravel was probably Ralph Vaughan Williams, who was his pupil for three months in 1907–08. Vaughan Williams recalled that Ravel helped him escape from "the heavy contrapuntal Teutonic manner ... Complexe mais pas compliqué was his motto."Vaughan Williams's recollections throw some light on Ravel's private life, about which the latter's reserved and secretive personality has led to much speculation. Vaughan Williams, Rosenthal and Marguerite Long have all recorded that Ravel frequented brothels. Long attributed this to his self-consciousness about his diminutive stature, and consequent lack of confidence with women. By other accounts, none of them first-hand, Ravel was in love with Misia Edwards, or wanted to marry the violinist Hélène Jourdan-Morhange. Rosenthal records and discounts contemporary speculation that Ravel, a lifelong bachelor, may have been homosexual. Such speculation recurred in a 2000 life of Ravel by Benjamin Ivry; subsequent studies have concluded that Ravel's sexuality and personal life remain a mystery.Ravel's first concert outside France was in 1909. As the guest of the Vaughan Williamses, he visited London, where he played for the Société des Concerts Français, gaining favourable reviews and enhancing his growing international reputation. 
Question: What was the name of the person that warned Manuel Rosenthal about studying Debussy?
Output (English): Ravel.