Answer:
B) the franc effectively became a gold currency.
Step-by-step explanation:
Before the price of gold plummeted, the French government could rely on bimetallism, but as the price of gold decreased and the value of silver remained the same, all you needed to do to earn some money was change your gold coins into silver coins (arbitrage). So the French government decided that it couldn't rely on the value of two different metals and chose gold.