Choose the set of figures which follows the given rule.

Rule: Closed figures losing their sides and open figures gaining their sides.

Choose the set of figures which follows the given rule.

Rule: Any figure can be traced by a single unbroken line without retracting.

Choose the set of figures which follows the given rule.

Rule: Closed figures gradually become open and open figures gradually become closed.

Choose the set of figures which follows the given rule.

Rule: Closed figures become more and more open and open figures become more and more closed.

Choose the set of figures which follows the given rule.

Rule: The series becomes complex as it proceeds.