Consider the incomplete Scala code where some types have been replaced with numbered question marks. def g (sString) = (string, string) - (...) val u. 71 - List (hello", "world").map (9) Which type must replace ? 1 for this code to typecheck correctly? 21 = List[List[String]] 21 = (List[(String, String)], List[(String, String) 1) ?1 = List[String ?1 = List[(String, String) ?1 = (List[String), List[String])