题目

如图所示的电路中,当S闭合时,电压表和电流表（均为理想电表）的示数各为1.6V和0.4A.当S断开时,它们的示数各为1.7V和0.3A, 求电源的电动势和内阻 答案：解：当S闭合时，R1和R2并联接入电路，得E=1.6+0.4r 当S断开时，只有R1接入电路，外电阻变大，得E=1.7+0.3r 两式联立得，E=2 V，r=1 ΩUnemployment in that country is likely to remain high in 2011, and ____ for the next few years.A. possibly B. necessarily C. gradually D. normally