Определить, чем являются в предложениях слова с ing окончанием-причастием,герундием или отглагольным существительным

1. You should think before speaking. (герундий)
2. After finding the new word in the dictionary, I wrote it down and went on reading.(герундий)
3. He spent much time on the copying lectures.(отглагольное сущ)
4. What do you mean by saying that?(герундий)
5. The students found the reading of English newspapers rather difficult at first.(отглагольное сущ)
6. Instead of going home after school, the girls went for a walk.(герундий)
7. Chalk is used for writing on the blackboard.(герундий)
8. We sat by the river-side listening to the running of the water.(причастие)
9. The cleaning of the room was done by the girls.(герундий)
10. Working in the garden is very good for the health of people.(герундий)
11. Going home from the cinema, they were discussing the play they had seen.(причастие)
12. Remembering that time was like going back to his childhood.(герундий)
13. Looking back upon that time, he realized how happy he had been then.(причастие)
14. You should think before speaking.(герундий)
15. The cleaning of the room was done by the girls.(герундий)
16. We sat on the sofa listening to music.(причастие)
17. The students found the reading of English newspapers difficult.(отглагольное сущ)
18. What do you mean by saying that?(герундий)

ing ...говый оборот))))

15 предложение -- точно не герундий, т. к. есть артикль, а значит это отглагольное существительное. то же самое и в 9-ом предложении.