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问题 填空题

直角三角形斜边的中线长是4cm，则它的两条直角边中点的连线长为______cm．

答案

因为直角三角形斜边上的中线等于斜边的一半，

所以斜边的长为2×4=8cm，

所以它的两条直角边中点的连线长为

1
2
×8=4cm．

故答案为：4．

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．names

B．cookies

C．software

D．extensions
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单项选择题

我国广泛使用的管螺纹是（）。

A、50°

B、55°

C、60°

D、70°
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