Ответ:
1) He doesn't know yet that we were in the summer camp. We had a very good time there. We walked, sunbathed, swam in the lake. Now my sister lives there. She will return home in 2 weeks.
2) She talks about her life since she returned from the camp. Since when has she been living with you? She has been living with us since September.
3) Show me what you write? I am writing a letter to a friend with whom I vacationed on the seaside in June. Does she often text you? Yes. We became real friends with her.