I write letters on Sunday
i am writting letters now
I will write letters next sunday
i wrote letters yesterday
i was writting letters,when you came
i will be writting letters at noon
i have written letters already
i had written letters sunday by the evening
i will have written letters by sunday
i have been writting letters for 1 hour
i had been writting letters since friday till sunday
i will have been writting letters for a day