We________on this project for four hoursLet’s have a rest

To keep safe,everyone________to wear a seat belt (安全带)in the car.

依次填入下面一段文字横线处的语句，衔接最恰当的一组是( )原来这董超、薛霸自从开封府做公人， ① ，回来被高太尉寻事，刺配北京。梁中书因见他两个能干，就留在留守司勾当。 ② 。

Only after my friend came .

The data shows the situations of the world economy ________ careful observation and detailed studies.[ ]