Complex sentence: Sergei Prokofiev wrote his Symphony No.2 in D minor (Op.40) in Paris in 1924-5, during what he called "nine months of frenzied toil".
Split into simpler sentences: Sergei Prokofiev wrote his Symphony No.2 in D minor (Op.40) in 1924-5. He wrote it in Paris, during what he called "nine months of frenzied toil".