下图为某一报告厅 * * 台的平面图,AB是讲台,S1、S2是与讲台上话筒等高的喇叭,

题型:计算题

问题:

下图为某一报告厅 * * 台的平面图,AB是讲台,S1、S2是与讲台上话筒等高的喇叭,它们之间的相互位置和尺寸如图所示。报告者的声音放大后经喇叭传回话筒再次放大时可能会产生啸叫。为了避免啸叫,话筒最好摆放在讲台上适当的位置,在这些位置上两个喇叭传来的声音因干涉而相消。已知空气中声速为340m/s,若报告人声音的频率为136Hz,问讲台上这样的位置有多少个?

考点:波的干涉
题型:计算题

阅读理解。

     Hello, my name is Cindy. I'm ten years old.  I live in Beijing with my family.  I have two brothers. They

  are twins. Their names are Bill and Victor. They are middle school (中学) students.Bill is in Class Two,

  Grade Eight.  Victor is in Class One, Grade Eight.

     Mike is my friend.  He likes soccer.  He is in the soccer club.  Bill likes soccer, too.  Sometimes he

 plays soccer with Mike. He wants to join the, soccer club.

     Mary is my twin sister. She likes painting. She is in the art club. She is interested(对……感兴趣)in

  Chinese history and she is a Beijing Opera fan. She often goes to see Beijing Opera with my father. She

 thinks she can learn about Chinese history.

1. _____ is a Beijing Opera fan.

    A. Mary    

    B. Mary's mother    

    C. Mike    

    D. Bob

2. Mary is interested in Chinese _____ .

    A. history    

    B. painting    

    C. dancing    

    D. people

3. _____  are twins.

    A. Mary and Mike    

    B. Bill and Mike

    C. Mary and Cindy    

    D. Mary and Bill

4. Bill likes _____ .

    A. art    

    B. music    

    C. soccer    

    D. ping-pong

5. Mary is in the _____ club.

    A. baseball    

    B. basketball    

    C. soccer    

    D. art

题型:计算题
如果矩形ABCD的对角线的交点与平面直角坐标系的原点重合,且点A和点B的坐标分别为(-
3
,2)
(
3
,2)
.矩形的面积为(  )
A.4
3
B.6
3
C.8
3
D.12
3
题型:计算题

There will be a twenty-minute break during the performance, ______ people can go to the restroom or buy some snacks.

A.that

B.where

C.when

D.which

题型:计算题

简述敏感性训练的目的。

题型:计算题

患者,男。胸前虚里处疼痛,痛连左手臂及小指,其病位当在

A.肺
B.胃
C.心
D.肝
E.肾

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