D. By 1963 we had 11,000........
The enumeration in the Constitution, of certain rights, shall not be construed to deny or disparage others retained by the people.
Francisco Pizarro
Manco Inca initially had good relations with Francisco Pizarro and several other Spanish conquistadors. However, in 1535 he was left in Cuzco under the control of Pizarro's brothers, Juan and Gonzalo, who so mistreated Manco Inca that he ultimately rebelled.
I think that the best answer to this is foreign investment: it was the one aspect which has helped Bulgarian economy the most.
The foreign investment is mostly connected to tourism - especially for example when rich western Europeans buy property in Bulgaria for private use.