As ________ birthplace of Huaxia civilization, Xi'an is ________ city with a long history and abundant cultural relics.
It is well understood _____ controls the flow of carbon dioxide in and out the atmosphere today.
–How far apart do they live? –_____ I know, they live in the same neighborhood.
He was about to tell me the secret _____ someone patted him on the shoulder.
He’s got himself into a dangerous situation _____ he is likely to lose control over the plane.
I have waited for her since _____.