(10分)为较精确地测量一只微安表的内阻，要求按照下图给出的电路进行测量。实验室中可供选择的器材如右表所示。实验中为了安全，电阻箱R的阻值不能取为零，只能为适当大小的阻值。则：

①实验中滑动变阻器应选用         ;

②将实物图连成实验电路。

③简述所需测量和记录的物理量：                                        ；

④用这些物理量表示内阻的测量值：                                  

—What does your friend  look like?  

—______.        [ ]

A. He is thin                          

B. She is a kind girl          

C. She likes music                      

D. She has a nice hat