A block chain is a data structure that stores time-ordered data in an ever-growing list, like an accounting ledger (分类账簿). The block chain data structure is maintained using a distributed, peer-to-peer network of computers with no central “master”. As with many new concepts, block chain technology generates much optimism and also a huge amount of interest and excitement. Just what is it good for?

In short, block chains may improve any process where people need to access, confirm, send or store information securely. This information could be a person’s identity, a product’s shipment history or digital property like money.

Typical databases, spreadsheets (电子数据表), and ledgers store information about objects, people, and the interactions between them. Much of the world’s information, from credit card transactions to medical and financial records, is stored in these types of systems.

These types of systems have considerable, well-documented weaknesses that arise from their being centralized. A centralized record is hard to understand and is exposed to unauthorized access or distribution. It is also, because it is a ‘master’ copy, exposed to permanent changing or deletion.

Block chains are also used to store information. Crucially, however, they differ in two ways.

First, information is parceled up into blocks and sealed. Bitcoin, for example, which is the most famous practical example of a production block chain, stores all transactions across the network every ten minutes or so in a single, newly formed block. Each block is then added to the previous one to form a chain.

Second, this “chain of blocks” is not stored centrally. Instead, each block is copied and distributed around an entire network of peers - be they individuals, public institutions, or businesses - using distributed ledger technology. (The terms “block chain” and “distributed ledger” are often used interchangeably; for the sake of clarity, block chain technologies tend to employ distributed ledger technology.)

Each time someone adds a new block to the chain, meanwhile it is added to everyone’s copy.

【小题1】What is the biggest strength of a block chain?

A．It promotes people’s enthusiasm about new technology.

B．It strengthens the security of processing information.

C．It enables people to store more data in time order.

D．It stores a large part of world’s information.

【小题2】The typical systems used to store information are weak in that ________.

A．they are difficult to operate	B．they can be accessed easily
C．they have a central “master”	D．they store considerable documents

【小题3】The passage is developed mainly by ________.

A．making comparisons	B．giving examples
C．making a list	D．showing the effect and causes

【小题4】What’s the author’s purpose in writing the passage?

A．To analyze the weaknesses of typical systems.

B．To encourage the popularity of the block chain.

C．To introduce the new concept of the block chain.

D．To compare the two different data structures.