题目

Kate heard a man's voice in the background, but she couldn't ___________ what he was saying. A. set aside         B. take back        C. make out        D. keep off 答案： C     一个空心小铁球放在盛水的容器中且置于铁棒AB的上方，绕在铁棒上的线圈接入如图电路中，开关S闭合后，小铁球仍浮在水面上，试在图中标出B端的磁极，并作出小铁球的受力示意图。