《河流冰情观测规范》(SL59—93)规定,测验河段内出现冰盖,且敞露水面面积小于河段总面积的()时为封冻。
A、25%
B、20%
C、30%
D、15%
参考答案:B
Before Chinese Chang'e-2, the US sent up a space probe to hit the moon to see _____. [ ]
A. whether there was water on it
B. whether was there water on it
C. whether on it was there water
D. whether was water on it
电压的国际单位是()。
A.伏特(V)
B.安培A.
C.欧姆(f1)
D.赫兹(Hz)