无髓牙变色（）
A.双氧水
B.麝香草
C.甲醛甲酚
D.浓台氏液
E.氢氧化钙制剂
参考答案：A
My friend was riding too fast and ______ the wall. Luckily he was not badly hurt. [ ]
A. knocked at
B. put into
C. crashed
D. knocked into
药材长螵蛸原动物是（）
A.银环蛇
B.大刀螂
C.小刀螂
D.五步蛇
E.巨斧螳螂
