Answer: The sentence that uses an adverbial clause to add variety and interest to its meaning is D) Although Drew wanted to download the latest video game, his parents refused to give him their permission to do so.
Explanation: An adverbial clause is a subordinate clause that acts as an adverbial in a sentence. An adverbial clause, which is introduced by a subordinating conjunction, cannot stand alone as a sentence since it does not express a complete thought; therefore, it is always preceded or followed by an independent clause. In sentence D), "Although Drew wanted to download the latest video game" is an adverbial clause since it has been introduced by the subordinating conjunction "although" and it does not express a full idea on its own. Moreover, it adds variety to the sentence because it is followed by an independent clause ("his parents refused to give him their permission to do so") and it also adds interest because to its meaning because the clause is expressing concession, that is to say that it is expressing an idea that suggests the opposite to what the main clause is indicating.