filter layer的用法和樣例：
例句
- It can be the filtration layer of the dikes,river canal,seacoast,concrete and retaining walls.
可以做堤壩，河渠，海岸，混凝土，擋土牆的過濾層。 - In drainage of agricultural lands, a filter or gravel envelope is used to prevent the entrance of fine sand and silt into the drains.
在農田排水中常常採用礫石或過濾層來防止粉細砂和泥沙進入排水溝。
