如图所示，导体框内有一垂直于框架平面的匀强磁场，磁感应强度B为0.12T，框架中的电阻R₁＝3Ω，R₂＝2Ω，其余部分电阻均不计，导体棒AB在磁场中的长度为0.5m，当AB以10m/s速度匀速沿着导体框移动时，试求：

（1）通过R₂上的电流I₂多大？

（2）保持棒AB匀速运动所需外力F多大？

Professor Lee's book will show you how you have observed that can be used in other contexts.

A．that you have observed

B．that how you have observed

C．how that you have observed

D．how what you have observed