The answer to your question would be that the sentence that does not use an adverb clause as a modifier is the following one: Without a clear goal, it is very difficult to make an effective plan. That is, the correct option would be B.
An adverb clause is a group of words that functions as an adverb in a sentence. As a clause, adverb clauses have a subject and a verb. On the contrary, phrases do not have a subject and a verb. Sentence B does not contain an adverb clause but a prepositional phrase as a modifier ("without a clear goal").
