_______ after a long walk,Henry called a
题型：选择题
问题：
_______ after a long walk,Henry called and said he couldn't come to the meeting.[ ]
A. Having worn out
B. Being worn out
C. To wear out
D. Worn out
题型：选择题
| 如图所示为一磁流体发电机示意图，A、B是平行正对的金属板，等离子体（电离的气体，由自由电子和阳离子构成，整体呈电中性）从左侧进入，在t时间内有n个自由电子落在B板上，则关于R中的电流大小及方向判断正确的是（ ） A．I= B．I= C．I= D．I=  |
