材料： Port State Control (PSC) is the inspection of foreign ships in national ports for the purpose of verifying that the condition of the ship and its equipment comply with the requirements of international conventions and that the ship is manned and operated in compliance with applicable international laws. The primary responsibility for ensuring that a ship maintains a standard at least equivalent to that specified in international conventions rests with the flag State and if all flag States performed their duties satisfactorily there would be no need for port State control. Unfortunately this is not the case as evidenced by the many marine accidents around the world - hence the need for additional control. The authority for exercising PSC is the national law based on relevant conventions. It is therefore necessary for a port State to be Party to those conventions and to have promulgated the necessary legislation before exercising PSC.In accordance with the provisions of the applicable conventions, Parties may conduct inspections of foreign ships in their ports through Port State Control Officers (PSCOs). 问题：The purpose of PSC is ______. ① to check and inspect foreign ships ② to verify the condition of a ship in compliance with requirements of international conventions; ③ to make sure that the ship is manned and operated well; ④to detain ships A.①② B.②③ C.①③ D.①②③④ Who will be responsible for ensuring that a ship maintains a standard at least equivalent to that specified in international conventions?A.PSCOs B.Ship owners C.Flag states D.Port states Before exercising PSC, a port state should______.A.become a contracting Party and promulgate regulations for implementing PSC B.inform ship owners C.establish procedures D.inform shipping companies PSC inspection is implemented by______ through______.A.flag states/PSCOs B.flag states/ship owners C.port states/PSCOs D.port states/ship owners