If China spends the money from buying US Treasury bonds on social security, how many years will China have social security?

No , you 're going the wrong way. I can't use the money to buy government bonds at home.

Because the foreign exchange used to buy government bonds belongs to the monetary category and is managed by the central bank; Social security and other inputs are under the jurisdiction of the Ministry of Finance. The Ministry of Finance cannot use the central bank's money. If it is equivalent to spamming money, it will lead to currency depreciation and price increase.

China implements the system of settlement and sale of foreign exchange, so the foreign exchange earned by foreign investors or China enterprises investing in China can't be used directly in China, and they need to be converted into RMB in the bank, so that the central bank will release the same amount of RMB when it receives the foreign exchange entering China. With the accumulation of these foreign exchange, it is necessary to maintain and increase the value of foreign investment, one of which is to buy US Treasury bonds.

The Ministry of Finance is the department that manages the income and expenditure of a country. Income comes from taxes, and expenses include civil servants' salaries, national defense, education, medical care and social security.

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Please indicate the source of the old uncle's works in cornfield.