Flammable, fire retardant and hard combustible flexible ducts all are combustible The flexible duct for air conditioning system must be made of non-combustible material是什么意思_Flammable, fire retardant and hard combustible flexible ducts all are combustible The flexible duct for air conditioning system must be made of non-combustible material在線(xiàn)翻譯_英語(yǔ)_讀音_用法_例句