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问题 不定项选择

如图所示，一带负电的滑块从粗糙斜面的顶端滑至底端时的速率为v，若加一个垂直纸面向外的匀强磁场，并保证滑块能滑至底端，则它滑至底端时的速率

[ ]

A．变大

B．变小

C．不变

D．条件不足，无法判断

答案

答案：B

单项选择题

Melissa and LoveLetter made use of the trust that exists between friends or colleagues.Imagine receiving an （） from a friend who asks you to open it. This is what happens with Melissa and several other similar email （） . Upon running, such worms usually proceed to send themselves out to email addresses from the victim’s address book, previous emails, web pages （） . As administrators seek to block dangerous email attachments through the recognition of well-known （） , 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 （） access to your network.

As administrators seek to block dangerous email attachments through the recognition of well-known （）.

A．names

B．cookies

C．software

D．extensions
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单项选择题

社会主义宏观调控的重点是（）。

A.正确处理经济发展同人口、资源、环境的关系

B.坚持改革开放

C.实行科教兴国

D.保持经济总量平衡和促进经济结构优化
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