It is five years since my dear aunt __________ here.

The air pollution is terrible.–It will be worse_______ we take action to protect the environment.

Never______ such a difficult problem. It took me almost half an hour to work it out.

__ your help, we can finish the task in time.

When you are reading, make a note of _______ you think is of great importance.（2006年东北八校联考题）