汽车电气设备的特点是（）、（）、（）、（）。
参考答案：低压直流；负极搭铁；单线制并联；两个电源
实行省（市）际联络线功率按区域控制偏差考核后，调频电厂具有调节能力时，电网频率应运行在（）范围内。
A、50±0.02Hz
B、50±0.04Hz
C、50±0.05Hz
D、50±0.1Hz
The minimum supply price, the lowest price at which a producer is willing to supply an additional unit of a good, is:（）
A. less than the marginal revenue for the additional unit.
B. the price at which producer surplus is maximized.
C. the marginal cost of producing the additional unit.
