请教一下两道SAT橘子改错题

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OG P659 T7：
the ragic story of Paolo and Francesca was the subject of a poem and a symphony, being popular throughout the nineteenth century.
A (as above)
B 错的
C the ragic story of Paolo and Francesca was popular throughout the nineteenth century, when it was the subject of both a poem and a symphony.
D 错的
E 错的
答案是C，我知道A有个being不好，但觉得C当中的when it叶有问题，请问这里的when是什么意思？谢谢

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还有：OC第三套section10 T12：Early American factories did not so much replace household manufacturing but complement it
B as complement
E as they were to complement
答案是B：It avoids the error of the original by using the appropriate conjunction "as" to complete the idea of the introductory phrase "so much" and thus properly link two parallel verbs ("replace" and "complement").
说replace和complement都是动词，但是原句中的did not so much后面怎么可以直接加动词？难道不应该是did not so much to + v.吗？
问题蛮多的。。谅解 谅解..