Select the figure from among the given options that can replace the question mark (?) in the following series.

From the first to the second box, the circle moved two steps and was placed just opposite the previous one.

From the third to the fourth box, the circle moved two steps and was placed just opposite the previous one.

Similarly, from the fifth to the sixth box, the circle will move two steps and will be placed just opposite the previous one.

By this logic options (b) and (d) can be eliminated.

In the squares of the first and fourth boxes, the line is completely outside.

In the squares of the second and fifth boxes, the line is partially inside and outside.

In the squares of the third and sixth boxes, the major part of the line will be inside.

By this logic option (c) can be eliminated.

Hence option (a) is the correct answer.