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.