The core concept here is that the sole measure of a country's success is not explicitly mentioned in the given knowledge points. However, the context suggests that it is related to economic factors. Option B directly refers to economic growth, which is a common indicator of success. Option A is related to research opportunities, which is not a sole measure. Option C, while important, is not mentioned as a sole measure. Option D is about education level, which is also important but not a sole measure. The correct answer is B because it aligns with the common understanding of a country's success.