The correct option is C Whether
A conjunction is a word which is used to connect sentences or clauses in the same clause.Option C)while is correct as it means a period of time and best suits the given sentence. The other options are wrong as weather, since, and unless indicate the state of the atmosphere at a particular place and time as regards heat, cloudiness, dryness, sunshine, wind, rain, etc,in the intervening period between (the time mentioned) and the time under consideration, typically the present, and except if (used to introduce the case in which a statement being made is not true or valid) respectively. The correct answer is C)while.