filter of graded density

例句：

1. 1. The filter is designed to remove impurities from the water.
   这个过滤器设计用来从水中去除杂质。
2. 2.The filter was made of fine mesh and could trap even the smallest particles.
   这个过滤器由细密的网制成，甚至可以捕捉到最小的颗粒。
3. 3. The filter is essential for maintaining clean drinking water.
   过滤器对于保持饮用水的清洁至关重要。