题目

—Can I ask you a question ______English? —Sure. A . for B . to C . about D . on 答案：C电阻R1的阻值为10欧，将它与R2并联后，总阻值为5欧，若将其串联，则总电阻为（　　）A．20欧B．15欧C．10欧D．5欧