Answer:
D) While the boys played football outside
Explanation:
An adverb clause is a group of words containing a subject and a verb whose function is to modify, describe or add more detail to an adjective, a verb or another adverb. This type of clauses are dependent, therefore, they do not express a complete thought.
Furthermore, an adverb clause often answer questions such as Why? How? When? Where? and In what circumstances? and is introduced by a subordinating conjunction like <em>while, after, since, although, as long as, because, before, even, even though, in order that, wherever, unless </em>and<em> until. </em>
The clause "While the boys played football outside" is an adverb clause because it has all the characteristics mentioned: it does not express a complete thought, it begins with a subordinating conjunction (<em>while</em>), it modifies the verb "danced" and it answers the questions <em>When did the girls dance in the living room?</em> Answer: <em>While the boys played football outside.</em>