(2014·石家庄高中复习教学质量检测)Seeing a large crowd at the street corner，I became aware of________unusual happening.

His plan, as well as Mary’s, sounds original. But the company, I think, won’t agree to __________ of them, for they are unrealistic.

I can’t go there with you; I have ______ to do.

One of the most important questions they had to consider was ______ of public health.

There isn’t ______ in the room.