根据三相电源和负载的不同情况，变压器初级和次级绕组可作Ｙ形和△形连接，一般容量不大而

阅读理解。

     Our school isn't very big, but it is very beautiful (漂亮). There are a lot of trees in it. I'm in Class Two,

Grade Seven. The walls of our classroom are white. There is a blackboard and some pictures on the wall.

Our classroom is very clean (干净). There are 45 students in my class. Mr. White is our English teacher.

He is from England. I like English very much. Mr. White is very friendly (友好) to us. He likes China and

he learns (学习) Chinese now. He can speak some Chinese. My father and mother are English teachers, too.

They often help me with my English. My classmates (同学) are very friendly. We are all friends. We like our

school class.

1. There are _________ in my school.

A. many trees

B. 45 students

C. two classes

2. Mr. White is __________.

A. an American teacher

B. my teacher

C. English

3. My father is _________ teacher.

A. my

B. a Chinese

C. an English

4. I like _________ very much.

A. English

B. my teachers

C. my friends

5. Our school is ___________.

A. not beautiful

B. not big

C. behind my home

在“测量小灯泡电阻”的实验中，滑动变阻器所起作用的说法不正确的是（　　）

A．改变电路中的电流

B．保护电路

C．改变被测小灯泡的电阻

D．改变被测小灯泡两端的电压

制作人体口腔上皮细胞临时装片，应先在载玻片上滴生理盐水，再放细胞．生理盐水的浓度是怎样的？（　　）

A．大于上皮细胞内液的浓度

B．小于上皮细胞内液的浓度

C．接近等于细胞内液的浓度

D．完全等于细胞内液的浓度

如果丹丹能在羽毛球锦标赛中出线，那么红红、宁宁和微微也会一起出线。如果以上断定是真的，则以下哪项也一定是真的

A．如果丹丹不能在锦标赛中出线，那么红红也不能出线。

B．如果红红、宁宁和微微一起在锦标赛中出线，那么丹丹也能在锦标赛中出线。

C．如果丹丹和宁宁能在锦标赛中出线，则红红和微微不能出线

D．如果宁宁不能在锦标赛中出线，那么丹丹也不能。

变压器有载分接开关检修时，切换开关过渡电阻无断裂，直流电阻阻值与产品出厂铭牌数据相比，其偏差值不大于（）。

A.±10%

B.±20%

C.±30%

D.±40%