Identify each italicized subordinate clause as a noun clause, an adjective clause, or an adverb clause. I will not repeat the story, since it is not true. (Since it is not true is italicized)

The italicized subordinate clause since it is not true is an adverb clause. Adverb clauses behave as simple adverbs would - they answer questions such as where, when, and why.

Why won't I repeat the story? Since it is not true.

Here the word since is used with the meaning because.