All parrots can learn to speak a few words and phrases. Not all parrots have equally pleasant dispositions, though some of those native to Australia can be counted on for a sweet temper. Almost any parrot, however, will show tremendous affection for an owner who raised the bird from a chick by hand-feeding it. If the statements above are true, then which one of the following must be true? ['If a parrot is not native to Australia, then it will be sweet tempered only if it is hand-fed as a chick.', 'Some parrots that can learn to speak are sweet tempered.', 'All species of pet birds that are native to Australia can be counted on for a sweet temper.', 'The sweetest-tempered parrots are those native to Australia.']