给下列的句子选择对应的问句或答句。 ( ) 1. It's only three o'clock. ( ) 2. What time? ( ) 3. On the playground? ( ) 4. Look at my dress. A. It's very pretty. B. No, in the gym. C. What time is it? D. At four o'clock.
【简答题】一台直流他励电动机,铭牌数据如下:PN=13kW,UN=220V,IN=68.6A,nN=1500r/min,起吊重物,在负载转矩时,运行在固一台直流他励电动机,铭牌数据如下:P N =13kW,U N =220V,I N =68.6A,n N =1500r/min,起吊重物,在负载转矩1000r/min时,运行在固有特性上,现采用能耗制动,试问:若采用电枢回路串电阻调速,应串入多大电阻?