Mimi said, "I have been writing this letter". (Change it into indirect speech) Mimi said that
Ashe had been writing that letter.
Bshe has been writing this letter.
Cshe had been writing this letter.
Dshe is writing that letter.
Ashe had been writing that letter.
Bshe has been writing this letter.
Cshe had been writing this letter.
Dshe is writing that letter.