所谓ξ电势就是指从滑动面到溶液内部过剩负电荷为零处的电位差。
参考答案：对
关闭一台运行Windows 98的计算机之前应先( )。
A．关闭所有已打开的程序
B．关闭Windows 98
C．断开服务器连接
D．关闭主机电源
Tim is in good shape physically（）he doesn't get much exercise.
A. if
B. even though
C. unless
D. as long as
