Exercise `1`:

`1.` was talking `-` arived

`2.` was crossing `-` saw

`3.` was sleeping `-` knocked

`4.` were watching `-` went out

`5.` was doing `-` was listening

`6.` was walking

`-` at 5 p.m yesterday afternoon `-` QKTD

`7.` was going `-` met

`8.` were you doing `-` came

`9.` Was he studying `-` arrived

`10.` were having `-` started

Exercise `2`:

`1.` was walking

`2.` was attending

`-` at this time last year `-` QKTD

`3.` was standing

`4.` was riding

`5.` were living

`6.` was walking

`7.` was going

`8.` was studying `-` were having

`9.` were dancing

`10.` were sitting

`______________________`

`@` When + S +  was/were + V_ing + O, S + V2/ed + O

`->` Diễn tả 1 hành động đang xảy ra thì 1 hành động khác xen vào

`@` While + S +  was/were + V_ing + O, S +  was/were + V_ing + O

`->` Diễn tả hai hành động xảy ra cùng một thời điểm trong quá khứ

`@` While + S + was/were + V_ing + O, S + V2/ed + O

`->` Diễn tả một hành động đang xảy ra, 1 hành động khác cũng đang xảy ra (hành động xen vào)