问题
选择题
When he looked up,he suddenly found himself________by a group of teenagers,________looked at
him anxiously. [ ]
A. to be surrounded; which
B. surrounded; who
C. be surrounded; who
D. having been surrounded; which
答案
答案：B
的匀强磁场中，导体棒AB的在金属框架上以
的速度向右滑动，已知导体棒
长为
，电阻为
，
，其他电阻不计，则导体棒端点