题目

The most valuable gift I have ever received was a photo album from my best friend Kevin.Kevin and I were classmates for all six years of primary school. We both had the same interests, so we always had a lot of things to talk about. It is wonderful to have such a good friend.However, last summer, Kevin had to move to another city because of his father's job. Then he gave me a photo album. It has photos of the memorable events we have experienced together. I've also written some notes under each photo, he said. I was deeply moved.I put the album beside my bed. I always look at it when I think o由欧姆定律I=UR，变形可得R=UI，则下列说法中正确的是（　　）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成反比C．导体的电阻跟电压和电流无关系D．当导体两端电压为零时，导体的电阻为零