通信电源中通常配置（       ）组蓄电池组
A、1
B、2
C、3
D、4

多项选择题直流电动机直接起动时，存在以下问题（ ）

单项选择题Which of the following is a characteristic of the Na+ K+ pump? A、It uses simple diffusion. B、No energy is necessary to operate the pump. C、It transports three Na ions out of the cell and transports two K ions into the cell. D、 It binds Na and K ions selectively. E、It helps to maintain equal concentrations of Na and K ions either side of the cell membrane.