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Currently, I use a grammar workbook to practice grammar. As I complete the book's exercises, I have come across a few sentences for which the explanations I do not understand. These sentences are:

1. There was a waning moon in the sky, and her radiance was not brilliant, but she was veiled in a thin cloud-curtain which seemed to diffuse and equalize it. (The book says the underlined element is an adverb clause. Is this correct and why? I think it is an adjective clause, modifing cloud-curtain.)

2. When, on his return from the villa (it was eleven o'clock), Winterbourne approached the dusky circle of the Colosseum, it occurred to him, as a lover of the picturesque, that the interior, in the pale moonshine, would be well worth a glance. ( the book's answers: prepositional phrase- adjective and adverb clause. My answers Adverb clause and I did not know.)
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1-- The which clause can indeed be considered an adverbial, modifying the whole predicate, was veiled in a thin cloud-curtain. (The whole process of veiling her diffuses, etc, her radiance.) I think a case could equally be made for its being a simple adjectival clause modifying cloud-curtain, however.

2-- The when clause could not possibly be a prepositional phrase, of course, since it has a subject (Winterbourne) and verb (approached); it is a sentence adverbial of time. Do you think the authors meant to underline just on...villa)?

That...glance is the delayed subject of occurred, following the introductory it.
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Thanks a bunch!
And so the editing began in earnest what sentence element is the underlined part, please?
And is a conjunction; so is a resultative (adverbial) conjunct. Some others: but nevertheless; or else; even though.
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