One of the Many "Rules of the Game" of the Gold

One of the many "rules of the game" of the gold standard order was:

A) all countries prohibit the movement of gold out of the country.
B) citizens be forced to sell all gold to the central bank, which would then issue new currency to pay for the gold and keep the gold in the vault to "back" the money in circulation.
C) silver be exchangeable for gold at a set ratio of the value of gold.
D) countries maintain money supplies that reflect the quantities of gold held by the central bank.