大型钢轨探伤车探测钢轨螺孔斜裂纹的探头折射角为（）。
A、70°
B、45°
C、37°
D、40°
参考答案：B
如果xy=100，x和y成______比例；如果8x=y，x和y成______比例．
—How much did the company donate to build the school library?
—About three ______ yuan.[ ]
A. million
B. millions
C. million of
D. millions of
