`23` was having / stopped
`24` were crossing / saw
`25`saw / was standing
`26` was reading / was learning / was doing
`27` were playing / came
`28` rang / was taking
`29` was / was walking
`30` was walking / saw
-> While / When+ QKD , QKTD : Diễn tả 1 hành động xen vào khi 1 hành động khác đang diễn ra trong quá khứ
-> While + QKTD , QKTD : Diễn tả 2 hành động đag xảy ra song song tromg quá khứ )
`31` have you studied ( How long has / have + S + Vpp+ O ? )
`32` have been waiting ( thì hiện tại hoàn thành tiếp diễn) / hasn't come ( thì hiện tại hoàn thành )
`33` have lived ( since 1975 - thì hiện tại hoàn thành )
`34` has read / Have you read ( thì hiện tại hoàn thành )
@ Dorris