A. 允许 B. 应缓慢 C. 禁止 D. 应小心
A. 正确 B. 错误
A. 口沟 B. 口器 C. 口腔 D. 嘴
A. the sinking of tail shaft B. the clearance of stern bearing C. the total flexure of shaft D. main engine crankshaft deflectio
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