Answer:
The adverb clause in the sentence <em>We're moving to Abilene if we sell our house</em> is<em> if we sell our house</em>.
Explanation:
An <u>adverb clause</u> is a dependent clause that plays the role of an adverb to modify an adjective, a verb or another adverb and that, as any other clause, includes at least one subject and one verb. <u>Adverb clauses</u> are grouped according to what they modify, such as place, purpose, time, cause, condition and more.
In the case of the sentence <em>We're moving to Abilene if we sell our house</em> , the adverb clause <em>if we sell our house</em> is introduced by <em>if </em>and, as a whole, modifies the verb <em>moving</em>.