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问题 选择题

下列说法①如果a=-13，那么-a=13，②如果a=-1，那么-a=-1，③如果a是负数，那么-a是正数，④如果a是负数，那么1+a是正数，其中正确的是（　　）

A．①③

B．①②

C．②③

D．③④

答案

①正确；

②如果a=-1，那么-a=-（-1）=1，则错误；

③正确；

④当a=-2时，1+a=-1，是负数，则错误．

则正确的是：①③．

故选A．

单项选择题

从保险公司经营活动看，保险赔偿与给付的基础是（）

A.保费

B.资本金

C.保险基金

D.保险保障基金
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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) .

A. memory B. cachesC. ports D. registers

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.
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