A chelating agent that softens hard tap water by binding with dissolved metal ions, preventing them from being deposited as a yucky residue on your nice clean dishes.
Hard dry food is really good for my teeth. it can help to remove the residue of food.
比较有硬度的干粮是对我的牙齿很好的食物，可以帮助清除牙垢。
3
The waste residue discharged from the production of compound phosphate fertilizer occupies large area of land and pollutes surrounding environment, which causes environmental problems hard to control.