题目

关于电场线的说法中,正确的是（    ）A.电场线既能描述电场的方向,也能描述电场的强弱B.电场线就是带电粒子在电场中运动的轨迹C.电场线是人们为了使电场形象化而假设的从正电荷出发至负电荷终止的曲线,它不是实际存在的线D.电场线是假设出来的一组曲线(或直线),所以它不能用实验方法来模拟 答案：ACBut for the fact that I an unexpected visitor, I _____to the lecture.A. had had/would goB. had/must goC. had/would have goneD. had had/must have gone