题目

Doreen Sykora is now a junior at McGill University. She had a difficult time when she first began college. She said, “I was always well prepared for my examinations. But when I go into class to take the exam, I would fall apart. I could just blank out because of nervousness and fear.” Hitoshi Sakamoto, an anthropology(人类学) student at Temple University in Tokyo reports similar experiences.These two young students were experiencing something called test anxiety. Because a student worries and is stressed about a test, his or her mind does not work as well as it usually does. The student如图2－4－11所示，a、b是位于真空中的平行金属板，a板带负电，b板带负电，板间场强为E.两板间的空间中加匀强磁场，方向垂直纸面向里，磁感应强度为B.一束电子以大小为v0的速度沿图中虚线方向射入，虚线平行于a、b板.要想电子沿虚线运动，则v0、E、B之间的关系应满足（　　）? A.v0=E/B?           B.v0=B/E?            C.?      D.图2－4－11