用方框中所给单词的适当形式填空。（每小题1分，共5分）

pour  seem  large  rapid  pollute

It ____________ that their living conditions were not very good.  
In the past twenty years, my hometown has developed ____________.
Our government has taken action to make the ____________ river clear again. 
There are several small chemical factories ____________ waste water into the river. 
At that time, China was the country with the ____________ population in the world.