The witnesses ________ by the police just now gave very different descriptions of the fight.
The driver ____ have drunk a lot before the accident, but I'm not quite sure of that.
When ____ to compare the education system of China and Britain, the professor gave no answer.
Why not get some work experience first ______ go straight on to university?
What if we meet with a situation _______ none of us are able to deal with?
His lack of professional knowledge _______for the failure of the experiment.