geometry
posted by Joel .
The measure of the side of rhombus GHIJ is equal to the measure of the side of square RSTU. Which statement about the two quadrilaterals must be true?
A. Their angle measures are equal.
B. Their diagonal measures are equal.
C. Their areas are equal in measure.
D. Their perimeters are equal.

Visualize a square sort of "squished".
The only thing that would remain constant is the perimeter.