1.Khi no dng du phy ?Khi danh t ng trc who ,which,whom... l :+ Danh t ring ,tnHa Noi , which ....Mary ,who is ...+ C this ,that ,these ,those ng trc danh t :This book ,which ....+ C s hu ng trc danh t :My mother ,who is ....+ L vt duy nht ai cng bit : ( Sun ( mt tri ) ,moon ( mt trng )The Sun ,which ...2. t du phy u ?- Nu mnh quan h gia th dng 2 du phy t u v cui mnh My mother , who is a cook , cooks very well- Nu mnh quan h cui th dng mt du phy t u mnh ,cui mnh dng du chm .This is my mother , who is a cook .3.Khi no c th lc b i t quan h WHO ,WHICH ,WHOM...- Khi n lm tc t v pha trc n khng c du phy ,khng c gii t ( whose khng c b )This is the book which I buy.Ta thy which l tc t ( ch t l I ,ng t l buy ) ,pha trc khng c phy hay gii t g c nn c th b which i :-> This is the book I buy.This is my book , which I bought 2 years ago.Trc ch which c du phy nn khng th b c .This is the house in which I live .Trc which c gii t in nn cng khng b which c .This is the man who lives near my house.Who l ch t ( ca ng t lives ) nn khng th b n c .4. Khi no KHNG C dng THAT :- Khi pha trc n c du phy hoc gii t :This is my book , that I bought 2 years ago. (sai) v pha trc c du phy -. phi dng whichThis is the house in that I live .(sai) v pha trc c gii t in - phi dng which5. Khi no bt buc dng THAT- Khi danh t m n thay th gm 2 danh t tr ln trong va c ngi va c vtThe man and his dog that ....That thay th cho : ngi v ch