Whenever work is being done, energy ______
题型：单项选择题
问题：
Whenever work is being done, energy ______ from one form into another.
A. converts
B. converted
C. is converted
D. is being converted
题型：单项选择题
．如图所示的电路中，电源电压恒定不变，R1=R2。当电键S1闭合、S2断开时，电流表、电压表的示数分别为I1、U1；当电键S2闭合、S1断开时，电流表、电压表的示数为I2、U2；则I1／I2 (17) 1， U1／U2 (18) 1（选填“＜”、“=”或“＞”）。