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问题 选择题

下列说法下列正确的是[ ]

A．强电解质的水溶液中不存在溶质分子，弱电解质的水溶液中存在溶质分子和离子

B．强电解质的水溶液导电性强于弱电解质的水溶液

C．强电解质都是离子化合物，弱电解质都是共价化合物

D．强电解质易溶于水，弱电解质难溶于水

答案

答案：A

单项选择题

The human nose is an underrated tool. Humans are often thought to be insensitive smellers compared with animals, (51) this is largely because, unlike animals, we stand upright. This means that our noses are (52) to perceiving those smells which float through the air, missing the majority of smells which stick to surfaces. In fact, (53) , we are extremely sensitive to smells, even if we do not generally realize it. Our noses are capable of (54) human smells when these are diluted to far below one part in one million.

Strangely, some people find that they can smell one type of flower but not another, (55) others are sensitive to the smells of both flowers. This may be because some people do not have the genes necessary to generate (56) smell receptors in the nose. These receptors are the cells which sense smells and send (57) to the brain. However, it has been found that even people insensitive to a certain smell at first can suddenly become sensitive to it when (58) to it often enough.

The explanation for insensitivity to smell seems to be that the brain finds it (59) to keep all smell receptors working all the time but can (60) new receptors if necessary.

57().

A.signs 

B.stimuli 

C.messages 

D.impulses
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单项选择题

Certificates are (16) documents attesting to the (17) of a public key to an individual or other entity. They allow verification of the claim that a given public key does in fact belong to a given individual. Certificates help prevent someone from using a phony key to (18) someone else. In their simplest form, Certificates contain a public key and a name. As commonly used, a certificate also contains an (19) date, the name of the CA that issued the certificate, a serial number, and perhaps other information. Most importantly, it contains the digital (20) of the certificate issuer. The most widely accepted format for certificates is X.509, thus, Certificates can be read or written by any application complying with X.509.

A．text

B．data

C．digital

D．structured
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