Answer: In sentence D. The veteran appeared proud as he saluted the flag, the adverb clause modifies an adjective.
Explanation: An adverb clause is a dependent clause that functions as an adverb. It cannot stand alone as a sentence because it does not express a full thought. Furthermore,<u> an adverb clause can be used to describe an adjective, a verb or another adverb.</u> For example<u>, in sentence D., the adverb clause is "as he saluted the flag"</u> since it is being introduced by the subordinating conjunction "as" and it does not express a full idea. Moreover,<u> this clause is modifying an adjective: "proud", which is immediately before it. </u>
