将所给句子中的一处错误找出并改正在横线上。
I was happy that my father promised buying a new computer for me.
____
为测量待测电阻Rx阻值,小敬设计了如图所示的电路,R0的阻值已知且电源电压不变,她____ (填“能”或“不能”)测出Rx的阻值,因为____ 。