问题
单项选择题
液环式真空泵是利用叶轮的（）形成大小不同的空间来达到吸气和排气的。
A、运动
B、旋转
C、独特结构
D、偏心安装
答案
参考答案：D
搜题请搜索小程序“爱下问搜题”
液环式真空泵是利用叶轮的（）形成大小不同的空间来达到吸气和排气的。
A、运动
B、旋转
C、独特结构
D、偏心安装
参考答案：D
| 阅读理解。 | ||||||||||||||||
| Some birthday customs are quite similar in many parts of the world---- birthday candles (蜡烛), birthday games，and birthday cakes. But some customs are more specific to certain countries. Here are some children talking about their customs. Linda---I am fourteen. I come from Aruba. In our country, Children take something special to school for their classmates and all teachers. Each teacher gives the birthday child a small gift like a pencil, an eraser or a postcard. The birthday child is also allowed to wear special clothes instead of the school uniform. Lucy---I am one year older than Linda. Denmark is my country. A flag is flown outside a window to show that someone who lives in that house is having a birthday. Presents are placed around the child's bed while they are sleeping so they will see them at once when they wake up. Tom---I am as old as Linda. I am from Brazil. The birthday child receives a pull on the earlobe (耳垂) for each year in my country. The birthday person also gives the first slice of cake to his/her most special friend or relative, usually mom or dad. | ||||||||||||||||
|