1 . 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.

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.

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

3. The passage is developed mainly by ________.

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

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.

2 . There is a boy called Bill in my gym class who has unbearably yellow teeth that almost make everyone feel unpleasant. Recently another boy told Bill that he should “go Ajax” his teeth. Bill was crushed. If the other boy had been thinking, he would have realized that there is a better way to handle such a situation. He could have dealt with it with tact. He could have showed this hurtful truth in a more careful, sensitive way-that's “tact”.

If a person isn't sensitive to another's feelings, there is no way he or she can be tactful. Yesterday, my 5-year-old brother proudly announced that he had cleaned the screen on our television set. Unfortunately, he used furniture polish, which produced an oily film on the television screen. My mother smiled arid thanked him for his efforts-and then showed how to clean the screen properly. Her sensitivity enables my brother to keep his self-respect. Yet, sensitivity alone does not make tact.

“Tactfulness” also requires “truthfulness”. Doctors, for example must be truthful. If a patient has just been disabled in an accident, a tactful doctor will tell the truth-but express it with sensitivity. The doctor may try to give the patient hope by telling them curing techniques under study or about advanced equipment now available. Doctors must use tact with patients' relatives as well. Instead of bluntly saying, “Your husband is disabled,” a doctor might say, “I'm sorry, but your husband has lost feeling in his legs and...”

Tact should not be confused with trickery. Trickery occurs when a nurse is about to give a patient an injection(注射) and says, “This won't hurt a bit.” Instead of trickery, the nurse might guarantee the patient that the discomfort of the injection is a small thing compared to the benefits of it. It would also be thoughtful for the nurse to tell the patients about some of these benefits.

Tact is a wonderful skill to have, and tactful people are usually admired and respected. Without tact our society would become an intolerable place to live in.

1. The underlined word “crushed” in the first paragraph probably means____.

A．surprised

B．cheated

C．regretful

D．painful

2. According to the author, his mother's praise for the brother is ____.

A．sensitive and tactful	B．sensitive but not tactful enough
C．truthful but not tactful enough	D．sensitive but ticklish

3. Which of the following shows the structure of the passage?
（The numbers stand for the paragraphs）

A．

B．

C．

D．