Answer:
The correct option is D.
Explanation:
From the given diagram it is clear that the numbers are written on the red circles and the blue circles are empty.
In options A and B, the number is written on the blue circle, therefore options A and B are incorrect.
By examining the series, it is clear that the sequence of color of circle is
Blue - Red
Red - Blue
Blue - Red
Now, we conclude that the next pair of circles must be Red - Blue.
In option C, the pair of circle is Blue - Red instead of Red - Blue, therefore option C is incorrect.
Only option is most likely the next step in the series.
Therefore the correct option is D.