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是什麼意思_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在線翻譯_英語_讀音_用法_例句