"Question tag" в плюсовой форме *sentence*, isn't it/aren't you/aren't we/isn't he/isn't she? В минусовой - *sentence*, is it/are you/are we/is he/ is she?
Если теория не интересует, то вот ответы -
He had a swim in the morning, isn't he?
It is a wonderful performance, isn't it?
There weren't any ticket's at the box office, were they?
The meeting wasn't over at 7 PM, was it?
It is cold outside, isn't it?
There weren't too many people in the park, were they?
They danced a lot, aren't they?
I am late, am I not? -- Тут важно уточнить, что в отличии от were, are, is и прочих местоимений, которые можно сложить с словом not, сотворив из него окончание "n't", ("weren't", "isn't" и т.д.) слово "am" с "not" не сливается.
Напиши "am'nt" и получи "2" за неграмотность.
These books are yours, aren't they?
I am not right, am I?