Observe the sequence of figures.
Which of the answer choices correctly completes the series?
Problem Figure:
1.
A square with a small black circle in the top-left corner.
2.
A square with a small black circle in the top-right corner.
3.
A square with a small black circle in the bottom-right corner.
4.
A square with a small black circle in the bottom-left corner.
5.
A square with a small black circle in the top-left corner.
6. ?