变频器是通过()的电源变换对异步电动机进行驱动的。
A、交流一交流一直流
B、直流一交流一直流
C、直流一直流一交流
D、交流一直流一交流
参考答案:D
小题1:The purpose(目的) of this notice is____________.
A.to ask people to visit the springs
B.to make visitors know the area
C.to tell visitors what not to do
D.to tell the visitors to have a rest小题2:The notice is written for____________.
A.visitors
B.children
C.workers
D.managers小题3:____________is NOT mentioned in the notice.
A.How long visitors can stay in the area
B.What visitors cannot bring to the area
C.Who looks after the visitors’ things
D.Whether smoking is allowed in the area小题4:The Chinese meaning for “slippery” is____________.
A.平坦的
B.湿滑的
C.狭窄的
D.冰凉的
有关水痘临床特征,下述哪些是正确的()
A.水痘为自限性疾病,约10天左右自愈
B.免疫功能低下者易形成播散性水痘,病情轻
C.妊娠早期感染水痘可能引起胎儿畸形
D.孕妇若发生水痘后数天分娩,亦可发生新生儿水痘
E.重症水痘可发生水痘肺炎,水痘脑炎等并发症