과거완료

12시제 1. I write a letter every day. 2. I wrote a letter every day. 3. I shall write a letter every day. 4. I have written a letter now. 5. I had written a letter then. 6. I shall have written a letter then. 7. I am writing a letter now. 8. I was writing a letter then. 9. I shall be writing a letter then. 10. I have been writing a letter now. 11. I had been writing a letter then. 12. I shall have..