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问题 单项选择题

ISDN基群接口的信道结构为30B+D，D信道的传送速率为（）。

A.64kbit/s

B.16kbit/s

C.4.8kbit/s

D.192kbit/s

答案

参考答案：A

单项选择题

Melissa and LoveLetter made use of the trust that exists between friends or colleagues. Imagine receiving an (16) from a friend who asks you to open it. This is what happens with Melissa and several other similar email (17) . Upon running, such worms usually proceed to send themselves out to email addresses from the victim’s address book, previous emails, web pages (18) .
As administrators seek to block dangerous email attachments through the recognition of well-known (19) , virus writers use other extensions to circumvent such protection. Executable (.exe) files are renamed to .bat and .cmd plus a whole list of other extensions and will still run and successfully infect target users.
Frequently, hackers try to penetrate networks by sending an attachment that looks like a flash movie, which, while displaying some cute animation, simultaneously runs commands in the background to steal your passwords and give the (20) access to your network.

A．cracker

B．user

C．customer

D．client
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单项选择题 A型题

地方性氟中毒主要是由什么原因引起的（）

A、食物氟污染浓度高

B、土壤中氟含量过高

C、饮水氟含量过高

D、饮水氟含量过低

E、维生素A缺乏和钙缺乏
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