The correct answer is 'Using the append() method for the host and service tuple.' The append() method is the most appropriate for adding a single item to the end of a list. It is efficient because it modifies the list in-place. The extend() method is not appropriate because it is designed for adding all elements from an iterable, which would break each tuple into individual elements and add them separately if not used correctly. The += operator can also add a tuple to a list, but it's an overkill operation for adding a single element, as it's more commonly used for concatenating lists. The insert() method with the index at the end is not wrong but less efficient and more verbose than the append() method.