题目

两电阻R1和R2 ， 它们串联后总电阻为12Ω，并联后总电阻恰好是 Ω．则R1=Ω，R2=Ω． 答案：【1】10【2】2We were on the point of discussing financial investment_____ the telephone rang unexpectedly. A. while                             B. when                       C. as                           D. once