Due to the Western Dramatic History, over the past 150 years musical theater has begun to evolve into its own genre.
Altering the harmony underneath the theme are the examples of thematic development. So,the correct answer is option b.
What is Thematic development?
A leitmotif, or theme, is formed by the musical technique known as "thematic transformation," which involves modifying the theme through permutation, augmentation, diminution, and fragmentation.
Franz Liszt and Hector Berlioz were principally responsible for its creation. In essence, the technique is one of variation. In essence, the technique is one of variation. A core theme is repeated repeatedly throughout a musical work, although it constantly changes appearances and takes on several opposing functions.
The architectural function of the sonata form in the classical symphony was to achieve "unity among variety," and this theme will always serve that purpose. Thematic transformation can support the emotionally charged phrases, richly coloured melodies, and atmospheric harmonies used by Romantic composers, which makes a difference in this instance.
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