故障按紧急和重要程度细分为三类，下面哪种故障不属于这三类（）
A.一般故障
B.重大故障
C.严重故障
D.紧急故障
参考答案：B
After living with his grandparents in the countryside for ten years, the boy returned to the big city ____ his parents worked.
A．which
B．where
C．that
D．when
踝关节跖屈内翻损伤容易伤及的韧带（）
A.腓距前韧带
B.腓距后韧带
C.腓跟韧带
D.下胫腓韧带
E.三角韧带
