Dear Larisa,
1. receive I … your letter about a month ago but I could not find time to write ever since.
2. be I … very busy lately, revising for my exams.
3. pass, work I … my first exam three days ago (it was English) and … non-stop revising for the second (Latin this time!) ever since.
4. sit Right now it is 7 p. m. and I … at my desk.
5. sit I … here for six hours doing my studying.
6. do Thank you for everything you … for me.