Identify the choice which features an adverbial clause accompanied by an independent clause. a) you don't know it, but you have already completed the most difficult part of the lesson. b) whether you know it or not, you have already completed the most difficult part of the lesson. c) you might not know it, but you have already completed the most difficult part of the lesson. d) you have already completed the most difficult part of the lesson, and you might not know it.