An adverb clause is a clause that act as an adverb. It means it can modifies an adjective, a verb or another verb. It contains three parts a subject, a predicate and a subordinate conjunction that keep it to be appear as a complete thought. In this while sick, is a subordinate conjunction that keep it to be a complete thought.
Thus, the correct answer is option C. adverb clause.
I know one thing that's helped me is being able to work on my own time. I'm able to work when I feel I am the most awake or I feel I can focus better. I'm able to follow a schedule that works for me.
