The correct answer is B) tapered, long blade, feeler gage. The tapered, long blade feeler gage is the best tool to use for measuring the rotor-to-stator air gap in electrical generation equipment because it can accurately measure the small clearance between the rotor and stator. Feeler gages are designed specifically for this type of precise measurement, whereas other tools like tape measures, dial indicators, or micrometers may not be able to access the tight space or provide the required level of precision. The other answer choices are not as suitable - a cloth tape measure would not have the necessary accuracy, a dial indicator may not fit in the confined space, and an inside micrometer would be too bulky to use in this application.