Eli built a 3-D model of a building, as shown below. Eli wrote the following calculation to find the volume. Which is a correct description of the error Eli made while calculating the amount of sand needed to fill the model?
A. He did not include the volume of the horizontal prism.
B. He did not include the volume of the vertical prism.
C. He included the volume of where the prisms overlap twice.
D. He included the volume of the entire horizontal prism twice.