Classify the underlined part of the following sentence by the type of phrase or clause it is.

European glass factories flourished after the Dark Ages.

a. adverb clause

b. adjective clause

c. adverb phrase

d. adjective phrase

I am going to assume that "after the Dark Ages" is underlined. If so, the correct answer is C. It cannot be any of the "clauses" since it isn't a clause - there is no verb present, so it must be a phrase. It is not an "adjective", since there is no noun which it modifies, but a verb "flourished". Therefore the correct answer has to be C, that is the only available option here.