题目

He looked quite healthy though he was __________. A. in seventy B. in his seventy C. at seventiesD. at the age of seventy 答案：D 解析: at the age of seventy 70岁；某人70多岁in one's seventies。 有两个电阻R1和R2，R1＞R2，在电源电压不变的前提下，在相同时间内，电流所做的功最多的连接方式是 [　　] A．单独将R1接在电路中 B．单独将R2接在电路中 C．将R1和R2串联接在电路中 D．将R1和R2并联接在电路中