C is the best answer because the notice belongs to the weeks, meaning you have to use an apostrophe to make "weeks" possessive. Think of it as "two weeks' worth of notice." This applies in other similar instances, like "He has three years' experience" or "It took me two hours' work." If you write "He has three years of experience," you do not need the apostrophe. (And, of course, there's no reason to hyphenate "two-weeks," as in D. Why attach "two" to "weeks"?)