A:①②
B:②③
C:①③
D:③④
如图所示,在两条平行的虚线内存在着宽度为L、场强为E的匀强电场,在与右侧虚线相距L处有一与电场平行的屏.现有一电荷量为+q、质量为m的带电粒子(重力不计),以垂直于电场线方向的初速度v0射入电场中,v0方向的延长线与屏的交点为O.试求;
Because Sarah has always saved __________, she is now able to afford a big house.
______ Mary ______ John has been to China before, but they know a lot about it.
盲人在“读”盲文时,依靠皮肤中的 ( )。