Clear cut answer not available in routine books, so it was subjected to multiple interpretations. accumulation of capital or tangible wealth can be done even by illiterate person if he has ownership over land or natural resources, so #1 1 or #3 do not necessarily mean Human capital formation. So answer could be b or c. Intangible wealth also includes patents and intellectual property rights- so if more patents are generated it shows population is more educated-pointing to human capital formation. UPSC has kept 'c' as the official answer.