逆行性牙髓炎的感染来源于
A．龋洞B．隐裂C．楔状缺损D．牙周病所致的深牙周袋E．磨损
参考答案：D
The students _____ are hard-working and ready to help others should be praised.
A．who
B．whom
C．which
D．whose
肌萎缩侧索硬化下列哪部位常首先受累（）
A.胸段脊髓
B.颈段脊髓
C.腰段脊髓
D.颈膨大前角细胞
E.以上均不正确
