`11.` He is poor.He has a very generous nature
`->`He, who has a very generous nature, is poor.
`12.`The author is an American.You are reading his book
`->`The author whose book you are reading is an American.
`13.`The girl feels happy.Her father has just won the first prize
`->`The girl whose father has just won the first prize feels happy.
`14.`We will tell you about the boy.You met his parents yesterday
`->` We will tell you about the boy whose parents you met yesterday.
`15.`Do you know the woman? Her daughter has won the contest
`->` Do you know the woman whose daughter has won the contest.
`16.`I like the house.It's walls were made of the glass
`->`I like the house of which walls were made of the glass.
`17.`I read about the child.His life was saved by his dog
`->` I read about the child whose life was saved by his dog.
`18.` The boy is a friend of mine.You are using his dictionary
`->`The boy whose dictionary you are using is a friend of mine.
`19.`Da Nang is a city. I was born and grew up there
`->`Da Nang is a city where I was born and grew up.
`20.`the room is very nice.i'm living in that room
`->`The room which I'm living in is very nice.