假定有一个用户表，表中包含字段：UserId（int）、UserName（varchar）、PassWord（varchar）等，该表需要设置主键，以下说法最恰当的是（）。

A:此表设计主键时，根据选择主键的最少性原则，最好采用UserId和PassWord作为组合主键。 B:此表设计主键时，根据选择主键的最少性原则，最好采用UserId作为主键。 C:此表设计主键时，根据选择主键的最少性原则，最好采用UserName和PassWord作为组合主键。 D:如果采用UserId作为主键，那么在UserId列输入的数值，允许为空。

Nowadays nearly everyone has suffered from a bad attack of forgetfulness when a password is needed.
The company computer. The home computer. Banking and ATM machines. Websites. Car and home security systems. The list goes on. It does not take long to accumulate a dozen or more passwords.
Scribbling them down on slips of paper or simply using the same password for anything and everything is how most people cope with the overload. The negative aspect of this is that either way makes it easier for hackers to invade computer privacy.
Researchers are now trying to do something about this by moving forward what may be an answer to the password puzzle-pictures.
What does the writer mainly talks about in the first three paragraphs

A:Why people are so forgetful in the computer era. B:what happens when many passwords are needed. C:Why hackers can easily invade computer privacy. D:What people usually do to solve the password puzzl

{{B}}第二篇{{/B}}

A:Its owner can change the ID code freely. B:Its user does not need to key in the ID number. C:It can record its user’s spoken password. D:It still can be used by someone else after being stolen.

{{B}}第二篇{{/B}}

A:It recognizes only its owner’s spoken password. B:It doesn’t need to work with an online server. C:It requires less ID information. D:It has a playback function.

{{B}}第三篇{{/B}}

A:Switching on the electronics to maximize the battery life. B:Pressing the "Say your password" button on the card’s surface. C:The password is verified. D:The ID squawk is sent to the server for it to identify.

第二篇 Credit Card Only Works When Spoken to A credit card that will not work unless it hears its owner’s voice could become an important weapon in the fight against fraud(欺骗)． The card requires users to give a spoken password that it recognizes using a built-in Voice-recognition chip．The idea is to prevent thieves using a stolen card or fraudsters using someone else’s credit card details to buy goods online． A model built by engineers at Beepcard in Santa Monica，California，represents the first attempt to pack a microphone。a loudspeaker，a battery and a voice?recognition chip into a standard．sized credit card． They are not quite there yet：the card is the length and width of an ordinary credit card，but it is still about three times as thick．The company now plans to make it thinner． The voice card is based on an earlier Beepcard technology designed to prevent fraud in online transactions This earlier card has no microphone，but has a built?in loudspeaker that it uses to“squawk”(发出叫声)a voice ID signal via a computer’s microphone to an online server． By verifying(证实)that the signal matches the card details，the server can establish that the user is not simply keying in a credit card number but actually has the card to hand．The ID code changes each time the card is used in a pre—ordered sequence that only the server knows． This prevents fraudsters recording the beeps，noting the card details and then playing back the audible ID when they key in the details later But this earlier technology cannot prevent fraudulent use of stolen cards The new one can The new voice card also identifies itself by its ID squawk．but it will not do this until it has verified the legitimate(合法的)user’s spoken password Thieves will be unable to use the card because even if they knew the password they would have to be able to copy the owner’s voice with a high degree of accuracy The challenge for Beepcard has been to develop voice-recognition and audio circuitry that Can be powered by a mini battery embedded(嵌入的)in a credit card．To maximize battery life，the electronics are only switched on when the card is being used．Pressing a button on the card’s surface prompts it to utter “Say your password ”in female voice If the voice—recognition software proves that the password is authentic(真实的)，it sends its ID squawk which the server then identifies．allowing the transaction to proceed Which of the following statements about the earlier card is true?

A:Its owner can change the ID code freely B:Its user does not need to key in the ID number． C:It can record its user’s spoken password． D:It still can be used by someone else after being stolen．

第二篇 Credit Card Only Works When Spoken to A credit card that will not work unless it hears its owner’s voice could become an important weapon in the fight against fraud(欺骗)． The card requires users to give a spoken password that it recognizes using a built-in Voice-recognition chip．The idea is to prevent thieves using a stolen card or fraudsters using someone else’s credit card details to buy goods online． A model built by engineers at Beepcard in Santa Monica，California，represents the first attempt to pack a microphone。a loudspeaker，a battery and a voice?recognition chip into a standard．sized credit card． They are not quite there yet：the card is the length and width of an ordinary credit card，but it is still about three times as thick．The company now plans to make it thinner． The voice card is based on an earlier Beepcard technology designed to prevent fraud in online transactions This earlier card has no microphone，but has a built?in loudspeaker that it uses to“squawk”(发出叫声)a voice ID signal via a computer’s microphone to an online server． By verifying(证实)that the signal matches the card details，the server can establish that the user is not simply keying in a credit card number but actually has the card to hand．The ID code changes each time the card is used in a pre—ordered sequence that only the server knows． This prevents fraudsters recording the beeps，noting the card details and then playing back the audible ID when they key in the details later But this earlier technology cannot prevent fraudulent use of stolen cards The new one can The new voice card also identifies itself by its ID squawk．but it will not do this until it has verified the legitimate(合法的)user’s spoken password Thieves will be unable to use the card because even if they knew the password they would have to be able to copy the owner’s voice with a high degree of accuracy The challenge for Beepcard has been to develop voice-recognition and audio circuitry that Can be powered by a mini battery embedded(嵌入的)in a credit card．To maximize battery life，the electronics are only switched on when the card is being used．Pressing a button on the card’s surface prompts it to utter “Say your password ”in female voice If the voice—recognition software proves that the password is authentic(真实的)，it sends its ID squawk which the server then identifies．allowing the transaction to proceed What is the advantage of the new voice card?

A:It recognizes only its owner’s spoken password． B:It doesn’t need to work with an online server C:It requires less ID information． D:It has a playback function

Most（）measures involve data encryption and password.

A:security B:hardware C:display D:program

Most （） measures involve data encryption and password.

A:security B:hardware C:display D:program