Concept:Customs and excise authorities manage the movement of goods across national borders.Explanation:They regulate imports and exports by checking goods entering and leaving the country.They also collect customs and excise duties and control bonded warehouses.These duties are meant to guard the economy and ensure compliance with trade laws.The core duty is therefore controlling the flow of goods in and out of the country.Answer:Option A — control of the flow of goods in and out of the country.