Final answer:
The diameter of the hole for a 10" diameter pole should be 12", per newer guidance suggesting up to 8 diameters of side-to-side spacing for sufficient room for tamping.
Step-by-step explanation:
The question relates to ensuring that there is sufficient room around a pole when setting it into a hole to allow for tamping. According to the 'rule of thumb' provided, the diameter of the hole should be larger than the diameter of the pole to provide adequate space. The diameter of the pole is given as 10 inches. Considering that newer work suggests as much as 8 diameters side-to-side is necessary for ample space, this would imply a hole diameter significantly larger than the diameter of the pole.
Given the options presented (8", 10", 12", 15"), the correct answer is c. 12". This answer allows for more than the minimum extra diameter on each side (1" on each side for a total of 2" extra diameter), which is closer to the guidelines provided. A choice of 15" would be even larger and exceed the requirement, but it is not one of the options presented.