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

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, 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, 3 contain a V-shaped element inside a geometrical figure.

2, 4, 5 contain two similar elements, one placed inside the other and touching it.

6, 7 contain geometrical figures which are divided into four equal parts by two mutually perpendicular straight lines.

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.