Which figure should replace the question mark (?) if the following series were to be continued?

Correct option is A

Given - 

figure first to second
the pair of letters (B), (O O O), (X X) shifts top to bottom in the next figure
similarly shifts in Figure third to fourth
Figures second to third
One element is removed in the top row and one element is added in the bottom row
in the missing figure, the top row should be 3 X
and the bottom row should be 3 O
middle row = double of previous figure middle row elements
in the fourth figure, the middle row element = 2
so in the missing figure it should be = 4

option a is correct.