Answer:
11. band
12. platoon
13. class
14. committee
15. bunch
Step-by-step explanation:
Collective nouns refer to names used for a collection of people or things. 
11. The band played a wonderful music in the park. 
12. A platoon of soldiers was deployed near the city hall. 
13. Our class will visit the TV station. 
14. The committee on programs did a good job. 
15. A bunch of keys was found under the tree.