They produced four reports, _______ of which contained any useful suggestions.
Here is so difficult a problem_______none of us can solve.
Is this museum _______ we visited last week?
It is not a serious illness. So I guess she will_______soon.
We never dared to ask him a question, _______ ?
It _______ . Some effort has been made to get DPRK to the table of six-party talk.