The________of the accident is still being looked into.
The best way to prevent the air polluting _____ , but the sky is still not clear.
--- What do you think of _____opening ceremony of the Guangzhou Asian games?----It was _____magical and memorable sight.
---Why don’t we go to the new Sichuan restaurant for a meal?-----_____
-----_____ leave at the end of this month.-------I don’t think you should do that until _____ another job.
He tried his best to solve the problem, _____ difficult it was.