Ответ:
An academy, an album, a bright album, an actor, a great actress, an arch, a marble arch, a chance, an unlucky chance, a dove, an ear, an elf, a tiny elf, a horse, an hour, a long hour, an institute, a lemon, a mill, an obelisk, an opera, an Italian opera, an owl, a paper, a rabbit, a quarter, a train, a wing, a voyage, a year.
Если слово начинается с согласной, то просто артикль а. Если с гласной, то an.
an hour - исключение