一台具有三对定子磁极的三相异步电动机，使用60Hz的交流电源供电_爱下问搜题

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问题单项选择题

一台具有三对定子磁极的三相异步电动机，使用60Hz的交流电源供电，则此电动机的旋转磁场转速为( )r/min。

A．1 000

B．1 200

C．1 500

D．1 800

答案

参考答案：B

完形填空

完型填空。

     Bill is an Australian  1 . He is twelve. He lives   2 his family in China. There are    3 people in his
family. His father Bill Clinton, his mother Catherine, his little sister Abbey and him. He has a yellow dog.   4   name is Barbi. Look! Abbey is   5 with Barbi. His father is mending his car. His mother is cleaning
the house. What is Bill doing? Ah, he is doing   6 homework in Chinese. He can't   7 Chinese well, but
he loves Chinese very much. Bill's   8  works in a middle school as an   9 teacher. His mother works at
a TV factory. Bill and his   10 go to the same school.

( )1.A. girl
(    )2.A. in
(    )3.A. three
(    )4.A. It's
(    )5.A. living
(    )6.A. his
(    )7.A. say
(    )8.A. father
(    )9.A. Chinese
(    )10.A. dog

B. boy
B. with
B. four
B. His
B. eating
B. its
B. speak
B. mother
B. Japanese
B. brother

C. toy
C. at
C. five
C. Its
C. playing
C. her
C. tell
C. Sister
C. English
C. sister

D. dog
D. on
D. six
D. Her
D. Drinking
D. their
D. talk
D. parents
D. French
D. mother

单项选择题

在成核－生长机制的液－固相变过程中，其成核过程有非均匀成核与均匀成核之分。将非均匀成核与均匀成核过程的成核势垒相比较，有如下关系（）。

A.非均匀成核势垒≥均匀成核势垒

B.非均匀成核势垒≤均匀成核势垒

C.非均匀成核势垒＝均匀成核势垒

D.视具体情况而定，以上三种均可能。