Only those who have experienced hardship ____ well aware of what happiness means.
| A．can they be | B．they can be | C．can be | D．they can |
When ____ to compare the education system of China and Britain, the professor gave no answer．
| A．ask | B．asking | C．asked | D．to ask |
Why not get some work experience first ______ go straight on to university?
| A．other than | B．rather than | C．more than | D．less than |
What if we meet with a situation _______ none of us are able to deal with?
| A．where | B．in which | C．what | D．that |
His lack of professional knowledge _______for the failure of the experiment.
| A．accounted | B．explained | C．counted | D．contributed |
Tom was about to close the window his attention was caught by a bird.
| A．when | B．if | C．and | D．till |