碳素工具钢是含碳量为0.65％-1.35％的优质高碳钢，其热处理后的硬度可达（）。
A. 60-64HRC
B. 70HRC以上
C. 50-55HRC
D. 200HBS以上
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在滑梁险槽的河心石梁尾部常有旺盛的（）下延，上行船可利用，以提高航速。
A. 夹堰水
B. 旺水
C. 回流
D. 斜流
Required lifesaving equipment on existing vessels may becontinued in use on the vessel if（）.
A. kept on board no more than 2 years
B. inspected and serviced every 6 months
C. destroyed if more than 5 years old
D. maintained in good and serviceable conditio
试衣间长、宽、高不宜小于（）
A. 900mmx900mmx1800mm
B. 900mmx1000mmx1800mm
C. 1000mmx900mmx1800mm
D. 1000mmx1000mmx1800mm
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