`16,` was mailing - was talking
`17,` was taking - came
`18,` was traveling - sank
`19,` was arrivinng - made
`20,` was walking - attacked
`21,` was living
`22,` did...do
`23,` was cooking
`24,` was cooking
`25,` were reading
⇒ Cấu trúc :
`1,` S + was/were + V_ing when S + V(past) + .....
`2,` S + was/were + V_ing while S + was/were + V_ing