Final answer:
The center-to-center distance of an 8" short radius return bend is 8 inches.
Step-by-step explanation:
The center-to-center distance of an 8" short radius return bend can be calculated by doubling the radius of the bend. In this case, the radius is half of the diameter, so it is 4 inches. Doubling the radius gives us a center-to-center distance of 8 inches (option a).