次级电流在触点从闭合到张开瞬间存在，以次级线圈为高压电源，以火花塞电极气隙为负载形成回路。
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点火提前角是指跳火时刻到该缸运行至压缩上止点时对应的曲轴转角
A. 对
B. 错
They are_____their clothes.
A. making
B. putting
C. put away
D. putting on
Listen! She____in the classroom.
A. is singing
B. sing
C. to sing
D. is sing
_____are the birds doing? They are singing in a tree.
A. Who
B. What
C. How
D. Where
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