电车公司维修站有5辆电车需要进行维修，如果用一名工人维修这5辆电车的修复时间分别为：10、15、8、6、13分钟。每辆电车停开1分钟损失10元。现在由2名工作效率相同的维修工人各自单独工作，要使经济损失减到最小程度，最少损失（）元。

A． 520

B． 820

C．840

D．1010

Melissa and LoveLetter made use of the trust that exists between friends or colleagues. Imagine receiving an (3) from a friend who asks you to open it. This is what happens with Melissa and several other similar email (4) . Upon running, such worms usually proceed to send themselves out to email addresses from the victim’s address book, previous emails, web pages (5) .

As administrators seek to block dangerous email attachments through the recognition of well-known (6) , 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 (7) access to your network.

3（）

A.attachment 

B.packet 

C.datagram 

D.message