The correct answer is: Option A) Because some people hunt it for its scales,
An adverb clause is defined as a group of words that act as an adverb to modify or describe verbs, adverbs, and adjectives. An adverb clause also requires a subject and a verb - just like a regular clause does -, and it must also start with a subordinating conjunction, such as Because, Although, As long as, etc.
Regarding the example provided by the question, all of the options start with a subordinate conjunction and have a subject, but only option A contains a verb: "hunt". The lack of verbs causes the rest of the options to be classified as adverb phrases, not adverb clauses.