`20`. No sooner had he stopped the car than one of the wheels exploded at once.
`->` Cấu trúc: No sooner + had + S + Vpp than + S2 + V2/ed
`=` Scarely had he he stopped the car when one of the wheels exploded at once.
`->` Cấu trúc: Scarely + had + S + Vpp + when + S2 + V2/ed
`21`. How long have they closed the factory?
`->` How long + have/has + S + Vpp ?
`=` How long is it since they closed the factory ?
`->` How long is it + since + S + V2/ed
