使用数字式氧气浓度计在ALARM档测定氧含量，当浓度低于（）时，蜂鸣器报警。
A. 19％
B. 18％
C. 17％
D. 16％
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The radiotelephone safety signal is（）.
A. securite repeated 3 times
B. safety repeated 3 times
C. pan pan repeated 3 times
D. securite securite repeated 3 time
Port of Registry refers to the port where（）.
A. the ship has been named
B. the ship has been built
C. the ship has been signed
D. the ship has been registered
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