类风湿关节炎的诊断标准中关于X线表现的最低要求是（）
A.骨质疏松和关节间隙变窄
B.关节畸形
C.关节间隙变窄
D.骨质疏松
E.骨性强直
参考答案：D
Attempting to get home before dark, ___________
A．Tom’s bike broke down on the way
B．it happened that Tom’s bike hit a car
C．a car knocked Tom off his bike
D．Tom knocked into a tree
釉质发育不全
A．牙齿发育异常
B．牙齿形态异常
C．牙齿结构异常
D．牙齿萌出异常
E．牙齿排列异常
