在牙嵌式应用最广泛的是（）
A.三角形齿
B.梯形齿
C.矩形齿
D.都不是
参考答案：A
My mother will go to the supermarket as soon as she _______ writing the letter. [ ]
A. finishes
B. finished
C. will finish
D. was finishing
霍尔点火信号发生器通过改变（）来产生电压信号的.
A.电流
B.磁感应强度
C.电阻
