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问题 单项选择题 A1型题

使人群易感性升高的因素是（）。

A.病原体毒力增强 

B.易感人口的迁入 

C.计划免疫 

D.传染病流行 

E.隐性感染后免疫人口增加

答案

参考答案：B

阅读理解
Saying goodbye to friends who are moving away is always hard. A Going-away Party can help to make everyone’s spirits bright and let your friends know how much you will miss them. We also have several other kinds of party invitations that my be suitable for a Going-away Party.
Invitation to a Going-away Party
Thursday, 19th March
Dear Joy and Mary,
You are invited to a farewell for the
“GREEN FAMILY’S VISIT TO AFRICA”
Departure (启程) date: 4th May
The best part of our big adventure to Africa will be when we come face-to-face with elephants, lions, crocodiles and other African wildlife. We have always wanted to do this.
Party given by: Mr and Mrs Green, Tom and John
Date: Saturday, 11th April 2013
Time: 5:00 p.m. to 10:00 p.m.
Place: 29 King Street, New Town, Sydney
Reply by: Thursday, 2nd April
Phone: 6458515
Food and drinks will be prepared at the party.
P.S. This event is NOT to be missed! We hope to see you there!
 
小题1:Who is the invitation sent to?
A．Mr and Mrs Green.B．Joy and Mary
C．Tom and John.D．Joy and John.
小题2:The party will take place on          .
A．19th MarchB．4th MayC．2nd AprilD．11th April
小题3:The Greens will go to Africa to          .
A．see some old friendsB．have a Going-away Party
C．see some African wildlife D．buy some food and drinks
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单项选择题 案例分析题

某110/35kV区域变电站，向附近的轧钢厂、钢绳厂及水泵厂等用户供电，供电方案如图所示。

图供电方案区域变电站110kV侧最小短路容量为1500MVA，35kV母线侧最小短路容量为500MVA，35kV母线的供电设备容量为25000kVA，轧钢厂用电协议容量为15000kVA。方案1：区域变电站以35kV分别向轧钢厂、钢绳厂及水泵厂等用户供电。轧钢厂设35/10kV专用变电站，以10kV向整流变压器供电。轧钢厂共设有两台4500kVA整流变压器，各供一套6脉动三相桥式整流装置，每台整流变压器10kV侧基波电流I1=225A，7次谐波电流的有效值按工程设计法计算。方案2：由于轧钢厂及钢绳厂合并为轧钢钢绳厂，并拟自建110/35kV专用降压变电站，改为110kV由区域变电站受电，轧钢厂整流变压器运行情况同上。假定不考虑轧钢厂其他谐波源，不考虑除7次谐波以外次数谐波，也无其他会放大谐波电流的容性负荷，请分别回答下列问题：

解释说明方案1中的电网谐波公共连接点应为下列哪项（）？

A.轧钢厂总变电站35kV母线C点

B.轧钢厂总变电站10kV母线F点

C.区域变电站35kV母线B点

D.区域变电站110kV母线A点
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