To what effect does shelley employ terza rima in "ode to the west wind"?

In P.B. Shelley's poem, Ode to the West Wind, we can observe his use of terza rima (rhyme scheme: a-b-a, b-c-b, c-d-c, d-e-d, ... Made famous by italian poet Dante Alighieri) to compose a set of 5 english sonnets. These sonnets, at the same time, are divided in cantos (italian form of chapters). By taking into consideration that P.B. was English living in Italy, we can conclude that his stylistic decision was to express his sense for unity in identity from England and Italy.

The correct answer is c. maybe