题目

Before you go to bed, you should say “__________” to your parents. A . Goodbye B . Good night C . How are you D . Good evening 答案：B电阻R1：R2=3：1，若将它们串联在电源两端，相同时间内电流做功之比W1：W2=     ；电功率之比P1：P2=        。