Consider the following Scala function definition.

 def f [X] (xs:List[X]) : List[X] = { xs match { case Nil => Nil case y::ys => y::(y::(f (ys))) } } 

If this function is executed on a list of length N, what is the length of the resulting list?

	N-1
	2N
	N
	2(N-1)