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问题 选择题

一个弹簧振子沿x轴做简谐运动，取平衡位置O为x轴的坐标原点．从某时刻开始计时，经过四分之一周期，振子具有沿x轴正方向的最大加速度．能正确反映振子位移x与时间关系的图象是（　　）

A．

B．

C．

D．

答案

由题，某一时刻作计时起点（t=0），经

1
4
周期，振子具有正方向最大加速度，则其位移为负方向最大，说明t=0时刻质点经过平衡位置向负方向运动，故C正确．

故选C

单项选择题

Melissa and Love Letter made use of the trust that exists between friends or colleagues.　Imagine receiving an (71) from a friend who asks you to open it.　This is what happens with Melissa and several other similar email (72) .Upon　running ,such worms usually proceed to send themselves out to email addresses from the victim’s address book, previous emails, web pages (73) .

　　As administrators seek to block dangerous email attachments through the recognition of well-known (74) ,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 (75) access to your network.

73（）

A．memory　　

B．caches　　

C．ports

D．registers
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单项选择题 A2型题

患儿，2岁。高热、咳喘9天后，潮热盗汗，面色潮红，口唇樱赤，干咳无痰，质红而干，舌苔光剥。其治法是（）。

A.养阴清肺

B.消肺止咳

C.止咳化痰

D.养阴益胃

E.益气健脾
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