用括号内所给动词的适当形式填空，必要时可加助动词或情态动词。

     Holly is an eighteen-year-old girl. She __1__ (finish) school last year. She __2__  (go) to a bank and

 worked as a bank clerk. Now she does well in her work. But she __3__ (want) to be a pianis. She likes

  playing the piano and she practices __4__ (play) the piano every day. She says she __5__ (be) a famous

  pianist in the future. And her parents agree with her.

某同学要测量一节旧电池的电动势和内阻，实验器材有一个电流表、一个电阻箱R、一个阻值为2Ω的定值电阻R₀，一个开关和导线若干，该同学按如图所示电路进行实验。

（1）电路中定值电阻R₀的作用是：　　　　　　　　　①                    。

（2）该同学为了用作图法来确定电池的电动势和内阻，若将R作为直角坐标系的纵坐标，则应取　　②　　作为横坐标。并利用实验数据在给出的直角坐标系上画出正确的图象。

（3）由图象可知，该电池的电动势E=    ③ V，内阻r=  ④  Ω；（保留两位有效数字）