Concept:Customs and excise authorities are government agencies responsible for regulating trade across national borders.
Explanation:The customs and excise authority controls the importation and exportation of goods.
It ensures that all goods entering or leaving the country comply with trade laws and regulations.
It also collects customs and excise duties on dutiable goods.
It manages bonded warehouses and keeps records of imported and exported goods.
These functions all point to regulating the flow of goods in and out of the country.
Option A is incorrect because transport systems are not provided by customs.
Option B is incorrect because port security is handled by other security agencies.
Option D is incorrect because dockyard repairs are not a customs function.
Answer:C. control of the flow of goods in and out of the country.