Joey is building a frame for a sandbox. The sandbox is going to be a quadrilateral that has the lengths shown. A rectangle is shown. The length of the top and bottom sides are 8 feet, and the length of the left and right sides are 12 feet. A diagonal that is 14 feet long is drawn from the bottom one corner of the rectangle to the other corner of the rectangle. Points X and C are opposite to the diagonal.

If the diagonal of the sandbox measures 14 feet, which best describes the shape of the sandbox?

a rectangle, because angle C is a right angle
a rectangle, because angle C and angle X are congruent
a quadrilateral, because angle C and angle X are acute
a quadrilateral, because angle C and angle X are obtuse