Во множественном числе:
feet,photos, families, potatoes, puppies, friends, countries, keys, dictionaries,men, fish.
под образец:
longer, shorter, more beautiful(образец не дан),slower, clever, quicker, better, worse, funnier.
под следующий образец:
the happiest, the slowest, the best, the biggest, the funniest,the largest,the shortest, the most beautiful,the most interesting,the worst.