I). Change the following sentences into passive voice.

1.Previous climbers had cut steps in the ice.

2.Soviet scientists are making wonderful discoveries.

3.The customs officer is counting the cases.

4.The director has just signed the letter.

5.The house agents showed us very nice flats.

6.The people gave him a hearty welcome. 

7.The people gave him a hearty welcome. 

8.The student read the text aloud

9.The teacher will correct the student’s composition.

10.The workers are unloading the steamer.

11.They are preparing the meal now

12.They don’t admit children under sixteen

13.They make these artificial flowers of silk.

14.They pay him regularly

15.They showed her the easiest way to do it.

16.They teach the children French and German.

17.They went home after they had finished the work.

18.They were taking more effective measures at the time.

19.They were throwing stones into the sea

20.This plant had fulfilled the yearly plan by the 15th November

Giúp mình với ạ,mình cảm ơn nhiều ạ