由于变极调速时接线与绕组排列的不同，电动机在不同极数时，输出转矩和功率有（）三种情况．
参考答案：恒功率恒转矩可变转矩
下列哪项不是蛛网膜下腔阻滞的适应证（）
A.上腹部手术
B.2～3小时以内的下腹部手术
C.短时间的盆腔手术
D.下肢手术
E.肛门或会阴部手术
Which of the following limits the ability of arbitrage to correct anomalies（）
A. Arbitrage is a relatively riskless activity, which has led to consistently reduced profits for many arbitrageurs, thereby reducing their interest in correcting market anomalies.
B. There is no guarantee that even correctly identified relative mispricing of similar stocks will be corrected in the near term.
C. Arbitrageurs are sophisticated traders but their short supply precludes the correction of market anomalies.
