机车信号机下方增设了两个ZS显示,用以表明当前接收信号制式是否为UM71或者ZPW-2000,为了防止混线造成ZS高电平,ZS采用闪亮输出,闪亮频率为()。
参考答案:20.3Hz
He was elected ______ president of the company, and _____ news came , in fact, as ______ surprise. [ ]
A. a; the ; /
B. /; the ; a
C. a; /; the
D. the; the; a
分解因式:
(1)x2y-4y;
(2)ax2-4ax+4a
(3)(x-y)2+4(x-y)
(4)(a2+b2)2-4a2b2.