II. Discourse Analysis 10%
      As Bitcoin, the world’s biggest cryptocurrency, keeps hitting record highs, crypto-mining has become
the latest global craze. But before you jump on the bandwagon and become a miner, it helps to have some understanding of blockchain, the record-keeping technology behind the Bitcoin network.
      Blockchain, sometimes referred to as Distributed Ledger(分類帳) Technology (DLT), is a specific type of database. __18__. As new data comes in, it is entered into a fresh block. Once the block is filled with data it is chained onto the previous block, which makes the data chained together in chronological order. Different types of information can be stored on a blockchain, but the most common use so far has been as a ledger for transactions. __19__. Decentralized blockchains are immutable, which means that the data entered is irreversible. For Bitcoin, this means that transactions are permanently recorded and viewable to anyone.
      Blockchain seems complicated, and it definitely can be, but its core concept is really quite simple. A
simple analogy for understanding blockchain technology is a Google Doc. When we create a document and share it with a group of people, the document is distributed instead of copied or transferred. __20__. No one is locked out awaiting changes from another party, while all modifications to the doc are being recorded in real-time, making changes completely transparent. Of course, blockchain is more complicated than a Google Doc, but the analogy is apt because it illustrates its critical ideas.
      While there are significant upsides to the blockchain, there are also significant challenges to its
adoption. Firstly, although blockchain can save users money on transaction fees, the technology is far from free. __21__. Also, blockchain is not efficient enough. Bitcoin is a perfect case study for the possible inefficiencies of blockchain. Bitcoin’s “proof of work” system takes about ten minutes to add a new block to the blockchain. __22__. Finally, while confidentiality on the blockchain network protects users from hacks and preserves privacy, it also allows for illegal trading and activity on the blockchain network. The most cited example of blockchain being used for illicit transactions is probably the   Silk Road   , an online “dark web” drug marketplace operating from February 2011 until October 2013 when it was shut down by the FBI.
      Despite its drawbacks, blockchain is still an especially promising and revolutionary technology because it helps reduce risk, stamps out fraud and brings transparency in a scaleable way for myriad uses. Just as the MIT Technology Review concludes, “The whole point of using a blockchain is to let people — in particular, people who don't trust one another — share valuable data in a secure, tamperproof way.”
(AB) This creates a decentralized distribution chain that gives everyone access to the document at the same time
(AC) It makes the history of any digital asset unalterable and transparent through the use of decentralization and cryptographic hashing
(AD) The “proof of work” system that bitcoin uses to validate transactions, for example, consumes vast
amounts of computational power
(AE) In Bitcoin’s case, blockchain is used in a decentralized way so that no single person or group has
control—rather, all users collectively retain control
(BC) With solutions to this issue being in development for years, there are currently blockchains that are
boasting over 30,000 transactions per second
(BD) It differs from a typical database in the way it stores information by keeping data in blocks that are then chained together
(BE) At that rate, it’s    estimated    that the blockchain network can only manage about seven transactions per second
【題組】18.