Final answer:
The most controllable factor causing hip dysplasia is Diet and Nutrition option (D), as it is something an individual can manage directly unlike genetic predisposition or aging.
Step-by-step explanation:
Among the factors that may cause hip dysplasia, the most controllable one is D) Diet and nutrition. While genetic predisposition, aging, and certain environmental factors can influence the development of hip dysplasia, diet and nutrition are aspects that an individual can manage more directly to potentially mitigate the risks associated with this condition. Proper nutrition can help maintain a healthy weight, thus reducing the stress on the hips and joints which may contribute to hip dysplasia, particularly in larger breeds of dogs or in overweight individuals.