题目

He didn’t keep on asking me the time any longer as he had had his watch _________. A. to repair      B. repaired       C. repairing      D. repair   答案：Bhave sth. done 让别人做某事  在图所示的电路中，电源电压为12V．闭合开关后，电流表的示数为0.4A，电压表的示数为8V，则电阻R2的阻值是________Ω．将滑动变阻器R1的滑片向右移动，电压表的示数将变________．