$ANSWER:$
11. The students were given a difficult arithmetic problem by the teacher.
13. The problem can be solved in just 2 minutes.
15. Nowadays electricity was used for light.
16. People who saw the robber in the bank yesterday are being interviewed by the police.
21. The books have been borrowed on wild animals.
22. That famous singer is noticed wherever he goes.
23. A house has just been bought with full comfort by their parents.
25. According to the inspector, the forest was burned down by lightning.
28. All the application form need to be filled by the students before living for summer holidays.
29. It was said that she was the most famous actress.
30. Milk is used for making butter and cheese.
