单项选择。
the last day of the holiday, we went home.[ ]
A. On
B. At
C. For
答案:A
下面关于齿轮说法中不正确的是()
A.同一条渐开线上各点的曲率半径是相等的
B.同一基圆上产生的渐开线形状相同
C.一对互相啮合的渐开线齿轮,其标准压力角相同
D.渐开线齿轮的标准压力角不依齿数变化而变化
—Could I speak to Mr. Hu , please ?
—_________ . He is having a meeting right now .
A. I think so
B.I don’t think so
C.I’m afraid not
D.Yes, go ahead