Picture three overlapping groups of four-sided figures: the group of all rectangles, the group of all rhombuses and the group of all squares. Which statement describes how the three groups sit inside one another?

A rectangle has four right angles; a rhombus has four equal sides. A figure with both properties has four equal sides and four right angles, which is precisely a square, and every square has both properties. So the square group is the overlap of the other two. The traps: rectangles are not all rhombuses (a 3 by 8 rectangle is not), the two groups certainly do overlap (every square is in both), and rhombuses are not all squares (a slanted rhombus has no right angle).