Good question. As far as I know the Government C miner would need to craft a policy related to their mining to restrict transactions from Government A; however, they would need a transaction identification method so what Government C says to do may be harder to implement. Also, although most mining is done by some majors there remains other smaller miners that would be outside the reach of Government C. Noting despite the financial sanctions on Russia at present, some sources indicate that they have settled some trades with Bitcoin.

Should a country build its own hash rate? I am for small government and would personally prefer they stayed out of #bitcoin but I do believe they should encourage individuals to mine Bitcoin and maybe businesses (or cooperatives of individuals - as they do with farming).