He asked a lot of questions, and none of ______ was easy to answer.
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 _____.