In the 1850s the French Franc Was Valued by Both

In the 1850s the French franc was valued by both gold and silver, under the official French ratio which equated a gold franc to a silver franc 15½ times as heavy. At the same time, the gold from newly discovered mines in California poured into the market, depressing the value of gold. As a result,

A) the franc effectively became a silver currency.
B) the franc effectively became a gold currency.
C) silver became overvalued under the French official ratio.
D) answers a and c are correct