If circumstances permit, use of layered multi-sand filter comprising both coarse sand and fine sand as filter materials fitted with automatic backwash self-cleansing device is desirable.是什么意思_If circumstances permit, use of layered multi-sand filter comprising both coarse sand and fine sand as filter materials fitted with automatic backwash self-cleansing device is desirable.在線(xiàn)翻譯_英語(yǔ)_讀音_用法_例句