When rectangle ABCD is rotated about side AB, the formed three-dimensional object is a cylinder.
Here's the reasoning:
- The height of the cylinder is the same as the height of rectangle ABCD, which is the vertical distance between points A and B. So, the height is 8 units.
- The diameter of the cylinder corresponds to the horizontal distance from D to C, which is the width of the rectangle. The width (or horizontal distance) from D to C is 5 units.
Thus, the correct identification of the three-dimensional object formed is a cylinder with a height of 8 units and a diameter of 5 units.
So the correct choice is: a cylinder with a height of 8 and diameter of 5 units.