Написать 3 предложения используя - was writing, was sitting, was having, bad bought, had flown, had started, sold, thought,understood (использовать все слова)

I was writing a letter when I undestood that I had not bought bread for dinner.
I thought that my brother had already started cleaning a room but when I came he was sitting on a sofa and was having a dinner.
I sold a balloon to that boy, next day when I met him, he said that it had flown as soon as he had left my house.