单项选择题 Before welding can be done in a tank that has carried petroleum products，a certificate must be obtained from（）.

单项选择题 At the same time，it is（）for you to signify your acknowledgement of the responsibility for the collision by signing the copies of this letter hereto attached and to return me two copies in due time.

单项选择题 At least one reinspection shall be made on each vessel holding a Certificate of Inspection valid for two years. This inspection shall be held between the tenth and fourteenth months of the duration period of the certificate and shall be（）.