Nearly everyone agrees that money doesn't buy as much as it used to, no matter when you want to spend it. This is certainly true of the paper money that passes so quickly through one's hands. But what about coins that seem to do very little except stay in purses and pockets? Unlike notes, metal money becomes more valuable the longer it is held, especially if it is put away where it won't get scratched or worn. Why is this? One reason is that coins, being more durable, fall more readily into a category for collectors. Naturally, the rarer gold pieces must become more valuable as the price of this metal goes up. But, curiously, one of the rarest coins in the world is not made of gold, but of the relatively cheaper silver. In 1840, the United States mint   struck 19570 silver dollars. That is what its records show. Today only six of this original number remain and these are unlikely ever to reach the auction   market. So what happened to some 19564 large silver coins, not the easiest sort of things to lose? One of the more romantic theories is that they were part of the payment to Napoleon for the American land then known as Louisiana. But they never reached France. Somewhere in the Gulf of Mexico, the ship transporting them was sunk, either by a storm or by pirates. The probable answer to the mystery is that they were melted down -- since the silver value was greater than the actual value of the coin. What really happened to the rest will probably always remain a mystery. What is known is that whoever can come up with one will find himself instantly rich. According to this passage, one of the rarest coins in the world is made of   _  .
silver gold copper paper
Question: Nearly everyone agrees that money doesn't buy as much as it used to, no matter when you want to spend it. This is certainly true of the paper money that passes so quickly through one's hands. But what about coins that seem to do very little except stay in purses and pockets? Unlike notes, metal money becomes more valuable the longer it is held, especially if it is put away where it won't get scratched or worn. Why is this? One reason is that coins, being more durable, fall more readily into a category for collectors. Naturally, the rarer gold pieces must become more valuable as the price of this metal goes up. But, curiously, one of the rarest coins in the world is not made of gold, but of the relatively cheaper silver. In 1840, the United States mint   struck 19570 silver dollars. That is what its records show. Today only six of this original number remain and these are unlikely ever to reach the auction   market. So what happened to some 19564 large silver coins, not the easiest sort of things to lose? One of the more romantic theories is that they were part of the payment to Napoleon for the American land then known as Louisiana. But they never reached France. Somewhere in the Gulf of Mexico, the ship transporting them was sunk, either by a storm or by pirates. The probable answer to the mystery is that they were melted down -- since the silver value was greater than the actual value of the coin. What really happened to the rest will probably always remain a mystery. What is known is that whoever can come up with one will find himself instantly rich. According to this passage, one of the rarest coins in the world is made of   _  .
A. silver
B. gold
C. copper
D. paper
Answer: