问题
单项选择题
All lifeboats，rescue boats，and rigid-type liferafts shall be stripped，cleaned，and thoroughly overhauled at least once every（）.
A.6 months
B.year
C.18 months
D.two years
答案
参考答案：B
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Ⅰ～Ⅱ度。面型较直。模型检查：上牙弓拥挤度7.5mm，下牙弓拥挤度4mm，Spee曲线曲度较深，一侧3mm，一侧5mm。X线检查：∠SNA＝82°，∠ANB＝1°，U1／PP＝112°，L1／MP=93°，MP／FH=35°。