A、$0. B、$1,216. C、$434. D、$864. B四个选项都表示金额，听音时需要特别留意表示价格的数字。录音末尾处提到比特币在网上交易的价格波动很大，2013年下半年一比特币的价格为1216美元，故B项为答案。根据录音，“比特币完全没有价值

Bitcoin is a digital currency used by terrorists and drug dealers, as well as major companies like Microsoft and Overstock.com. In other words, everyone from private individuals who order pizza to terrorists who order weapons.
    Bitcoin was a currency created in 2009 by a mysterious software developer. He calls himself Satoshi Nakamoto. No one has ever met him, and it is not clear if he is one person or several people.
    Bitcoin does not use printed money. It is digital only. The currency is created on computers by a community of people across the globe. Anyone can join that network, or group, according to Coindesk.com.
    This network processes transactions made with the digital currency. Bitcoins are stored in a "digital wallet" over the Internet or on the user’s computer.
    There is not an unlimited amount of bitcoins. Nakamoto set up rules to limit the currency to 21 million bitcoins.
    With bitcoins, there are no banks or fees. Users do not register with their real names. Merchandise can be bought without the user showing her or his identity. Bitcoins are not taxed or regulated anywhere in the world.
    Bitcoins have become the currency of choice for people online buying drugs or other illegal activities. For example, bitcoins are being used by ISIS terrorists to fund operations, according to Ghost Security Group. It is a counter-terrorism network that focuses on the Internet and social media, Morgan Wright is a cyber security expert and senior fellow at the Center for Digital Government, a national research and advisory institute on information technology policies.
     [20]"Terrorists need anonymity." Wright told Fox News. "Countries have gotten very good at tracking terror financing in the years since 9-11. Networks have looked for new ways to do it, and it appears they’ve found it in bitcoin."
    Despite this dark side of the new currency, bitcoins have their supporters. More and more merchants are beginning to accept bitcoins.
    Some people buy bitcoins as an investment, hoping they’ll increase in value. There are many online marketplaces that allow people to buy and sell bitcoins using different currencies. Coinbase, in San Francisco, runs the world’s largest bitcoin exchange, and operates 2.8 million bitcoin wallets globally, according to Wired. You can also buy and sell bitcoins on Bitquick, Xapo, and CoinCorner, among other exchanges.
    It is possible to do complex financial trades with bitcoins, such as futures, options and swaps. The price of bitcoins on online exchanges has fluctuated widely, which has led to speculation in the digital currency. In 2009 and early 2010. bitcoins had "no value at all" said Wired. Then in late 2013. it reached a high of $1,216. As of now, the price of one bitcoin is about $434.
19. What do we learn about bitcoin?
20. Why are bitcoins favored by terrorists according to Morgan Wright?
21. Who runs the largest bitcoin exchange in the world?
22. What was the price of one bitcoin in late 2013?