Sure! Here are the sentences transformed into negative and interrogative forms:

6. **Affirmative:** Tom went to the hospital to provide food two weeks ago.
**Negative:** Tom did not go to the hospital to provide food two weeks ago.
**Interrogative:** Did Tom go to the hospital to provide food two weeks ago?

7. **Affirmative:** The sidewalks were wet after the rain.
**Negative:** The sidewalks were not wet after the rain.
**Interrogative:** Were the sidewalks wet after the rain?

8. **Affirmative:** I started to work as a volunteer three years ago.
**Negative:** I did not start to work as a volunteer three years ago.
**Interrogative:** Did I start to work as a volunteer three years ago?

9. **Affirmative:** They were in the library an hour ago.
**Negative:** They were not in the library an hour ago.
**Interrogative:** Were they in the library an hour ago?

10. **Affirmative:** Tom and his friends went to orphanages to learn English yesterday.
**Negative:** Tom and his friends did not go to orphanages to learn English yesterday.
**Interrogative:** Did Tom and his friends go to orphanages to learn English yesterday?