`1` While I was enjoying my holiday in Dubai , I met one os my old classmates .

`-` While/When + S + was/were + V_ing + O , S + V(quá khứ) + O : Trong khi ai đó đang làm gì , ai đó đã làm gì .

`2` 

`@` When Lan dropped by our house , we were having our dinner .

`@` While we were having our dinner , Lan dropped by our house .

`-` While/When + S + was/were + V_ing + O , S + V(quá khứ) + O : Trong khi ai đó đang làm gì , ai đó đã làm gì .

`3` While they were having dinner , they were discussing .

`-` While + S + was/were + V_ing + O , S +was/were + V_ing + O : Trong khi ai đó đang làm gì , ai đó đang làm gì .

`4` While her father was abroad , he had more freedom .

`-` While/When + S + was/were + V_ing + O , S + V(quá khứ) + O : Trong khi ai đó đang làm gì , ai đó đã làm gì .

`II.`

`2.`

`-` When Lan dropped by our house, we were having our dinner.

`-` While we were having our dinner, Lan dropped by our house.

`3.` While they were having dinner, they were discussing the problem.

`4.` While her father was abroad, he had more freedom.

`--------------`

`@` hành động đang xảy ra thì một hành động khác chen ngang:

When + S + Ved/V2, S + was/were + V-ing

While + S + was/were + V-ing, S + Ved/V2

`@``2` hành động diễn ra song song cùng một thời điểm trong quá khứ:
While + S + S + was/were + V-ing, S + was/were + V-ing