Task: Question Answering
Input (English): Passage: During his lifetime it was above all as a master of orchestration that Ravel was famous. He minutely studied the ability of each orchestral instrument to determine its potential, putting its individual colour and timbre to maximum use. The critic Alexis Roland-Manuel wrote, "In reality he is, with Stravinsky, the one man in the world who best knows the weight of a trombone-note, the harmonics of a 'cello or a pp tam-tam in the relationships of one orchestral group to another."
For all Ravel's orchestral mastery, only four of his works were conceived as concert works for symphony orchestra: Rapsodie espagnole, La valse and the two concertos. All the other orchestral works were written either for the stage, as in Daphnis et Chloé, or as a reworking of piano pieces, Alborada del gracioso and Une barque sur l'ocean, (Miroirs), Valses nobles et sentimentales,  Ma mère l'Oye, Tzigane (originally for violin and piano) and Le tombeau de Couperin. In the orchestral versions, the instrumentation generally clarifies the harmonic language of the score and brings sharpness to classical dance rhythms. Occasionally, as in the Alborada del gracioso, critics have found the later orchestral version less persuasive than the sharp-edged piano original.In some of his scores from the 1920s, including Daphnis et Chloé, Ravel frequently divides his upper strings, having them play in six to eight parts while the woodwind are required to play with extreme agility. His writing for the brass ranges from softly muted to triple-forte outbursts at climactic points. In the 1930s he tended to simplify his orchestral textures. The lighter tone of the G major Piano Concerto follows the models of Mozart and Saint-Saëns, alongside use of jazz-like themes. The critics Edward Sackville-West and Desmond Shawe-Taylor comment that in the slow movement, "one of the most beautiful tunes Ravel ever invented", the composer "can truly be said to join hands with Mozart". The most popular of Ravel's orchestral works, Boléro (1928), was conceived several years before its completion; in 1924 he said that he was contemplating "a symphonic poem without a subject, where the whole interest will be in the rhythm".Ravel made orchestral versions of piano works by Schumann, Chabrier, Debussy and Mussorgsky's piano suite Pictures at an Exhibition. Orchestral versions of the last by Mikhail Tushmalov, Sir Henry Wood and Leo Funtek predated Ravel's 1922 version, and many more have been made since, but Ravel's remains the best known. Kelly remarks on its "dazzling array of instrumental colour", and a contemporary reviewer commented on how, in dealing with another composer's music, Ravel had produced an orchestral sound wholly unlike his own. 
Question: What does Ravel have play in six to eight parts while the woodwind are required to play with extreme agility?
Output (English): his upper strings.