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单选题
20. The officer in charge of the navigational watch shall notify the master immediately (). ①if good visibility is encountered or expected; ② if difficulty is experienced in maintaining course; ③ if the ship meets any hazard to navigation, such as ice or a derelict.
A
①②
B
①③
C
①②③
D
②③
答案解析
正确答案：D
解析：
解析: 负责航行值班的高级船员应立即通知船长的时机:保向操作存在困难;船舶遇到航行危险物, 如冰或遗弃物。
