铁路的坡道值用()表示。
A.十进制
B.百分数
C.千分数
D.万分数
参考答案:C
The experiment shows that proper amounts of exercise,if _____ regularly,can improve our health. [ ]
A. being carried out
B. carrying out
C. carried out
D. to carry out
选用的消弧回路所用的反向二极管,其反向击穿电压不宜低于()。
A.1000V;
B.600V;
C.2000V;
D.400V。