The answer is: HIGH POROSITY.
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(although low permeability can be associated with greater water retention. Permeability can be affected by particular size. For instance, larger particular have larger poles, so fluid (water) can pass through water quickly (higher permeability and less water retention). As such, smaller particles have smaller pores, so fluid (water) can pass through water LESS quickly (lower permeability and RETAINING MORE WATER.).
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However, "high porosity" is the best choice.
Most populated city is Tokyo and most populated country is China
In the western front, they used Trench Warfare Method
In Trench Warfare the opposing teams would build some sort of trench surrounding their defended area to prevent the the opposing team in invading their protected Area. It's best used as a Defensive method which require the armies to stay hold and defended their position. That's why they're not moving so much
