This is his daughter.（复数句） These are their daughters.
Those are keys.（单数句） That is a key.
David is my brother.（一般疑问句 ） Is David your brother?
Is Tony her brother?（作肯定回答） Yes,he is.
Is she your aunt?（作否定回答） No,she isn't.
Those are your parents.（一般疑问句） Are those your parents?
This is （my mother）.（对括号部分提问）Who is this?
This is my cousin.（His）name is Alan.
She is my aunt.（Her）son is Tony.
（Those）are my books.
Are these your （parents)
Are （these）his sisters?
（Is）that your computer?