Final answer:
The adverb clause in the sentence "In the third century C.E., the Romans encountered trouble wherever they turned." is 'wherever they turned.' This clause modifies the main clause by indicating where the trouble was encountered and begins with the subordinating conjunction 'wherever.' The correct option is c. Wherever they turned.
Step-by-step explanation:
The student has asked to identify the adverb clause in the sentence: "In the third century C.E., the Romans encountered trouble wherever they turned." An adverb clause is a group of words that function as an adverb. This means that the clause modifies a verb, an adjective, or another adverb in the sentence. Adverb clauses typically answer questions such as when, where, why, with what goal, or under what conditions. They also begin with a subordinating conjunction (e.g., wherever, although, because, when), which links them to the independent clause of the sentence.
Looking at the options provided, the phrase In the third century C.E. sets the time and acts as a prepositional phrase. The phrase The Romans encountered trouble is the main clause of the sentence and does not function as an adverb. The full sentence The Romans encountered trouble wherever they turned includes the main clause and the adverb clause, but it is not itself the adverb clause.
Therefore, the correct adverb clause is c. Wherever they turned, which modifies the main clause by explaining where the trouble was encountered. It is set off by the subordinating conjunction 'wherever,' which begins the clause and indicates its adverbial nature.