Đáp án:
1. How long / it / take / you / go / school / ?
⇒ How long does it take you to go to school ?
2. Annie / clever / get / airport / early / .
⇒ Annie is clever to get to the airport early.
3. The plane / delay / for an hour / the bad weather / .
⇒ The plane was delayed for an hour because of the bad weather.
4. Not open / door / unless / you / be / sure / who / visitor / be / .
⇒ Don't open the door unless you are sure who the visitor is.