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问题 单项选择题

窦性PP间距逐渐缩短，继而出现一个长PP间距，最长PP间距＜最短PP间距的2倍，应考虑

A．窦性停搏
B．二度Ⅱ型窦房阻滞
C．窦性心动过缓
D．病态窦房结综合征
E．二度Ⅰ型窦房阻滞

答案

参考答案：E

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. virtual B. virus C. wormsD. bacteria

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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单项选择题

旅游者在旅游活动的初期阶段，通常表现出的心理状态有( )。

A．求新心理、求全心理

B．求安全心理、懒散心态

C．求安全心理、求新心理

D．求全心理、懒散心态
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