The best description of the economy of Country X is C. mixed economy.
In a mixed economy, there is a combination of both state control and individual entrepreneurship. In this case, the state-owned company controls the production and sales of natural resources (indicative of command economy characteristics), while there are small businesses thriving in other sectors (suggestive of market economy traits). The presence of government restrictions and heavy taxes also indicates a mixed system where both the government and private entities play significant roles.