无极继电器由()与接点系统两大部分组成。
参考答案:直流电磁系统
I have never dreamed of _______ for me to win the first prize in the 1000-meter race.
A.there was a chance
B.there being a chance
C.it being a chance
D.it was a chance
(x2+1)(x-2)7的展开式中x3的系数是_______。