阅读理解。

     This is our classroom. It is a nice big room. The windows are big and the walls are white. There is a blackboard

on the front wall. There is a map on the back wall. It's a map of China.

     Under the blackboard there is a big desk. It's for our teachers. There are fifty desks and chair in the room. They

are for us students.

     What's on the teacher's desk? There are many flowers on it. They are for our English teacher. We like her. She is

a good teacher.

1. Our classroom is _______________

A. small                        

B. big                    

C. old                    

D. new

2. There's a ________ on the back wall.

A. clock                

B. picture          

C. map            

D. guitar

3. There're ___________ students in our class.

A. 35                    

B. 40            

C. 45              

D. 50

4. The teachers' desk is _____ the blackboard.

A. on                 

B. in                

C. under          

D. for

5. Our English teacher is a ________

A. woman              

B. man            

C. boy            

D. policeman

双代号网络中关键工作是指（）工作。

A、总时差为零；

B、自由时差为零；

C、总时差最小；

D、自由时差最小