未知题型 More than a million persons live within 2,000 miles of the North Pole in an area that includes most of Alaska, Siberia, and Scandinavia—a region rich 40 forest and mining industries. Apart from a handful weather stations, within the same distance of the South Pole is not a single tree, industry or settlement.

单项选择题 认证中班前会评价属于（）

判断题 电流比变压器电桥平衡时，三个绕组的磁通大小相同，相位相反。