We__pay anything/The concert is free
a. mustn't b. didn't need c. don't need to

1

Объяснение:

Они не обязаны платить за концерт тк он бесплатный

1 - c2 - a3 - f4 - e5 - b

6 - d 

1) was developed 

2) were all invented

3) were improved

4) are used

5) is brought

6) were sent

7) will predicted

8) will predicted