Group the given figures into three classes using each figure only once.

1, 5, 7 have two similar elements, one inside the other.

2, 4, 8 have one element placed inside a different element.

3, 6, 9 have two similar elements, one inside the other and the area between the two elements is shaded.

1, 4, 7 are all (two-dimensional) quadrilaterals.

2, 5, 8 are all three-dimensional figures.

3, 6, 9 are all (two-dimensional) triangles.

1, 2, 3 are figures composed of two straight lines.

4, 5, 6 are figures composed of three straight lines.

7, 8, 9 are figures composed of four straight lines.

1, 6, 9, are all triangles.

3, 4, 7 are all four-sided figures.

2, 5, 8 are all five-sided figures.

1, 3, 9 have one element placed inside a different element.

2, 5, 6 contain two mutually perpendicular lines dividing the figure into four parts.

4, 7, 8 have two similar elements (unequal in size) attached to each other.

1, 2, 5 are figures that have patterns formed from four lines curved in a concave direction.

3, 7, 8 are figures that have patterns formed from four lines curved in a convex direction.

4, 6, 9 are figures that have patterns formed from these straight lines.

1, 5, 7 contain a rectangle with its two diagonals as the outer element and another element (similar or different) placed inside it.

2, 6, 9 contain a triangle with its three medians as the outer element and another element (similar or different) placed inside it.

3, 4, 8 contain a circle with its two mutually perpendicular diameters as the outer element and another element (similar or different) placed inside it.

1, 3, 5 are figures having partially or completely curved boundaries.

2, 6, 8 are all triangles.

4, 7, 9 are all quadrilaterals.