A lot of trees ______ on the hill yester
题型：选择题
问题：
A lot of trees ______ on the hill yesterday. [ ]
A. are planted
B. will be planted
C. have been planted
D. were planted
题型：选择题
| 如图所示，矩形线圈有N匝，长为a，宽为b，每匝线圈电阻为R，从磁感应强度为B的匀强磁场中以速度v匀速拉出来，那么，产生的感应电动势和流经线圈中的感应电流的大小应为（ ） A．E=Bav， B．E=NBav， C．E=Bav， D．E=NBav，  |
