Перефразируйте, употребляя притяжательный падеж the flat of my sister, the son of her mother, the name of tnis man, the mark of our student, the work of those men, the sister of my friend, the parents of that boy, the room of these people, the food of those dogs, the hobby of these gentlemen, the voice of this singer, the friend of susan, the foot of the animal, the ball of my child
my sister's flat, her mother's son, this man's name,our student's mark, those men's work, my friend's sister, that boy's parents, these people's room, those dogs's food, these gentlemen's hobby, this singer's voice, Susan's friend, animal's foot, my child's ball