Answer:
The adverb clause is "unless they were given the chicken first" and it has been introduced by the subordinating conjunction "unless". The word modified is the verb "wrestle".
Step-by-step explanation:
Adverb clauses, also known as adverbial clauses, are dependent clauses that function as adverbs. As they are dependent clauses, they must have a subordinating conjunction that connects to the rest of the sentence. In this case, the adverb clause gives information regarding how things would happen. It states a condition: The green and greasy alligators would wrestle if they got the chicken first.