Ответ:

1.When the police arrived, the car had gone

2.George finished doing his homework at eight o’clock

3.When she got to the shop, it had closed

4.The train had left when he came to the station

5.We had eaten everything by the time he arrived at party

6.I knew that he hadn't learnt the poem

7.When they left the beach, the rain had already started

8.Arthur didn't know that we had already arrived

9.When I came, I saw that mother had cooked dinner

10.My friend studied English before he had entered the institute

11.The car had gone when I looked into the street

12.He took the decision before I had come

13.Nick had returned from office by seven o’clock

14.We got to the stadium at four o’clock but the game had already started

15.She came at six o’clock

16.I thought that my parents had already returned

17.He was sure that we hadn't recognized him

18.Did you find your key which you had lost before?

19.Meg said that she had been in this city

20.The doctor arrived when we had already helped him