def random_string_in(arr)
      return nil if arr.empty?
      index = random_number(0, arr.length-1)
      arr[index]
    end
def random_string_in(arr)
      return nil if arr.empty?
      index = random_number(0, arr.length-1)
      arr[index]
    end
Return a random string in a rangeof pre-defined strings