牙本质来自于
A．牙板B．牙囊C．牙 * * D．成釉器E．上皮根鞘
参考答案：C
心肺脑复苏时治疗室性心律失常最常用的药物是（）
A.阿托品
B.胺碘酮
C.利多卡因
D.肾上腺素
E.碳酸氢钠
We usually have supper at six o'clock, but _____ we do at 6:30. [ ]
A. all the time
B. at one time
C. at times
D. on time
