Which number will replace the question mark (?) in the following series? 729, 243, ?, 27, 9, 3

Which number will replace the question mark (?) in the following series? 729, 243, ?, 27, 9, 3

A.            54

B.            78

C.            81

D.            36

Sol:

Pattern follows here is 1/3 latter number is of former number.

Required number =243/3

=81