用于直流供电回路的自动空气开关，可以采用交流开关代替。

阅读理解

       Take any long piece of paper. Now glue the ends of the paper together. You have made a ring.

       Take a second long piece of paper. Twist the paper once and glue the ends together. Now you

have made a Mobius band. For people studying maths, this band is uncommon.

       This strange band was first made in the 1800s by a German man named August Mobius. Mr. Mobius studied maths. He wanted to find a way to show how this band works with maths. Understand it or not,

this band has only one surface. You can find this out for yourself.

       If you draw a line on the surface of the paper before you twist and glue it, the line is only on one side

of the paper. The paper has two surfaces. However, if you draw a line after you make the Mobius band,

you can follow the line around all sides of the paper. In other words, the Mobius band must have only

one surface.

       It is also very interesting to see what happens when you cut the band. If you cut the Mobius band in

half once down the line you drew, you do not get two Mobius bands. Instead, after you cut the band, it

turns into one large twisted ring. Then, if you cut this ring in half along the middle of the band again, you

get two connected  Mobius bands.

       Try it!

1. What is a Mobius band?

A. A ling piece of paper.

B. A paper ring for people to wear.

C. A metal ring for music.

D. An interesting twisted ring.

2. How can you change the two surfaces of a long piece of paper into one surface?

A. Glue the ends of the long piece of paper.

B. Cut the two surfaces of the paper into one.

C. Draw a line in the middle of the paper.

D. Twist the paper once and glue the two ends.

3. What do you get if you cut the Mobius band along the middle?

A. A long piece of paper.

B. Two long pieces of paper.

C. Two Mobius Bands.

D. One large twisted ring.

收到某单位预付货款存入银行，引起的变动是（）。

A．一项资产增加，一项负债增加

B．一项资产减少，另一项资产减少

C．一项资产增加，一项所有者权益增加

D．一项资产减少，一项所有者权益减少

以下对于基尔霍夫第一、第二定律说法正确的是（）。

A．仅适用于直流电路

B．不仅适用于直流电路，还适用于交流电路

C．仅适用于线性交、直流电路

D．适用于所有电路的分析（包括线性、非线性；交、直流；暂态、稳态等）

已知在25℃、101.3Kpa下，1摩尔CH₄气体充分燃烧放出热量为890KJ，写出该反应的热化学方程式______，计算若燃烧1立方米CH₄气体应放出热量为多少KJ？______小明家每月平均用15立方米CH₄气体，一年消耗的热量为多少KJ？______．（甲烷体积已折算为标准状况下）

Criticism without suggesting areas of improvement is not ______ and should be avoided if possible.

A. constructive
B. productive
C. descriptive
D. relative