韶山3型4000系电力机车主电路的供电方式是()供电。 ["A、转向架独立","B、集中","C、单台电机独立","D、分散"]
地球的平均曲率半径为()km。
锑盐易水解析出沉淀,取样后应立即加盐酸酸化至()保存。 ["A.含酸达1%","B.pH≤1","C.pH≤2","D.pH≤3"]
天然水中锑的浓度平均约为()μg/L;天然水中铋的浓度在()μg/L左右。 ["A.0.01,0.1","B.0.02,0.2","C.0.1,0.01","D.0.2,0.02"]
望远镜产生视差的原因是()。
通过()海水面的水准面称为大地水准面。