题目

______ it have been the failure to pick up directions from the ground control that caused the air crash?   A. Must                  B. Could                       C. Would                  D. Should 答案：B对式子R=U/I的理解，下面的说法中正确的是（　　）A．导体的电阻跟它两端的电压成正比B．导体的电阻跟通过它的电流强度成反比C．导体的电阻跟它两端的电压和通过它的电流强度无关D．加在导体两端的电压为零，则通过它的电流为零，此时导体的电阻为零