口服对肠内外阿米巴病均有效的药物是
A．甲硝唑
B．依米丁
C．氯喹
D．喹碘方
E．巴龙霉素
参考答案：A
如图所示电路，R1=R3=R4=2Ω，R2=1Ω．当电键S断开时，电压表的示数为2.8V，当电键S闭合时，电压表的示数为2.5V，求：
（1）画出S断开时的等效电路图，求出外电路电阻值．
（2）画出S闭合时的等效电路图，求出外电路电阻值．
（3）电源电动势和内电阻各是多少？
A lot of research and studies have shown that Trench oil, taken out from kitchen waste, ______ the increase of cancers.
A appeals to B. attends to C. contributes to D. devotes to
