Concept: Nigeria's development is mainly limited by weak investment capacity rather than by secondary effects like migration or reliance on oil.
Explanation: Many problems affect Nigeria's development, but the root issue is low capital formation.
Low capital formation means the country cannot generate enough savings and investment.
This limits the building of industries, infrastructure, and job creation.
Poor developmental policies and oil dependence are serious, but they result from or worsen the lack of investable funds.
Thus, the major obstacle among the options is low capital formation.
Answer: A. low capital formation