连接管螺纹所用的填料线缠绕不需要考虑旋向。
参考答案:错
What's wrong with him? I haven't seen him_____ last Wednesday. [ ]
A. since
B. on
C. by
D. until
一个代表大数字的符号左边附一个代表小数字的符号,就表示大数字加上小数字的数目。