From the Kata Description:

Preloaded for you is a function say_list which receives an array as its only argument and has the following behaviour:

say_list(["Apple"]) // => "Apple"
say_list(["Apple", "Orange"]) // => "Apple or Orange"
say_list(["Apple", "Banana", "Dragonfruit", "Kiwi"]) // "Apple, Banana, Dragonfruit or Kiwi"

You may find this function useful when implementing one of the methods of one of the classes in this Kata.