1. This is Mr.hung . I was telling you about him ( whom )
$->$ This is Mr.Hung who was being told you about by me.
2. The chair is broken . I bought the chair yesterday ( which )
$->$ The chair which I bought yesterday is broken.
3. The old man is my grand father . He lives next door ( who )
$->$ The old man who lives next door is my grand father.
CHÚC BẠN HỌC TỐT !!!!!!!!