r by accident or ___________,he arrivedtoo late to help us.

The level of __________ in the river was falling.

Every possible means ________ to prevent the air pollution，but the sky is still not very clear

he college entranceexamination near, both the parentsand the students are more and more anxious

Where did the accident happen? — It was at the post office near the hotel _____the peace talk would be held [ ]