1. Form opposite adjectives using un-, im-, ir-, in-

Решение:

1. impossible
2. unbelievable
3. irresponsible
4. unbalanced
5. inactive
6. illegal
7. unusual
8. unreal
9. unhealthy
10. unforgettable

Ответ: impossible, unbelievable, irresponsible, unbalanced, inactive, illegal, unusual, unreal, unhealthy, unforgettable.