The population _________ of that country is 500 per square mile.
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We need a _________ of ten people to play this game.
The busy traffic entrance was a __________ to pedestrians.
The factory closure is __________ inevitable.
虹吸滤池是由（ ）格单元滤池所组成的一个过滤整体，称为“一组（座）滤池”
A. 1-5
B. 6-8
C. 9-12
D. 13-16
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