一男孩跌倒时腕关节屈曲，手背着地受伤，致桡骨下端关节面损伤，腕骨移位方向是( )
A．向掌侧
B．向背侧
C．向尺侧
D．向桡侧
E．向背侧、尺侧
参考答案：A
解析： 桡骨远端关节面骨折伴腕关节脱位者称为Barton骨折。跌倒时腕关节屈曲、手背着地，骨折时腕骨向掌侧移位；若跌倒时腕背伸，前臂旋前位，撞击桡骨关节背侧发生骨折，腕关节向背侧移位。
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If every student who was in the eleventh grade in 1996 and who used a computer in school at least once a week used a computer at least once a week in 1997, and if 20% of those students who were in the eleventh grade in 1996 and who did not use a computer in school at least once a week, did use a computer in school once a week in 1997, then what percent of twelfth-graders in 1997 used a computer in school at least once a week
A．(A) 40%
B．(B) 50%
C．(C) 60%
D．(D) 70%
E．(E) 80%
