Consider the following Scala function definitions: def f [X, Y] (a:Option[X], g:X=>Y) : Option[Y] = { a match { case None => None case Some (x) => Some (g (x)) } } def index [X] (xs:List[X], n:Int) : Option[X] = { xs match { case Nil => None case y::ys if (n == 0) => Some (y) case _::ys => index (ys, n - 1) } } What is the output of running: f (index (List (10, 11, 12), 5), (n:Int) => n * 2)