Which of these sequences is a geometric sequence?
O A. 1,2,4,7, 11, 16, 22, ...
O B. 2, 4, 8, 14, 22, 38, ...
O c. 3, 6, 9, 12, 15, 18, 21, ...
OD. 3,9, 27,81, 243,729, ...