问题 单项选择题

Melissa and LoveLetter made use of the trust that exists between friends or colleagues. Imagine receiving an (56) from a friend who asks you to open it. This is what happens with Melissa and several other similar Email (57) . Upon running, such worms usually proceed to send themselves out to Email addresses from the victim’s address book, previous Emails, Web pages (58)
As administrators seek to block dangerous Email attachments through the recognition of well-known (59) , 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 (60) access to your network.

A.memory

B.caches

C.ports

D.registers

答案

参考答案:B

填空题

人类为探索物质的组成、性质和变化,经历了漫长的历程.请阅读下列信息:

信息1:数十亿年来,地球上的物质不断地变化.大气的成分也发生了很大的变化.下表是原始大气和目前空气的主要成分:

空气的成分N2、O2、CO2、水蒸气及惰性气体等
原始大气的主要成分CH4、NH3、CO、CO2
信息2:下图分别是海水和人体中部分元素的质量分数.

根据上面提供的信息,运用你学过的有关知识回答下列问题:

(1)在海水中,金属元素含量最高的是钠元素. 我国青海湖是个内湖,其湖水是不能流到大海中,湖水与海水相似也是咸的,而地球上多数的湖水是淡的.从物质在水中溶解的规律和水的天然循环的角度看,海水中钠元素的含量比较高的原因是______.

(2)水中氧元素的质量分数比海水中氧元素的质量分数(填“大”或“小”)______.                    

(3)原始大气是指绿色植物出现以前的大气.假设把现代的人或其他的动植物放在原始大气中,你认为他们能否生存下去?______,原因是______.

(4)绿色植物出现以后,原始大气中的CO2逐渐减少,同时O2逐渐增加的原因是______.

(5)随着原始大气中O2缓慢地增加,CH4、NH3、CO等气体逐渐被氧气氧化而缓慢地减少,使大气的成分逐渐演化成现代大气.原始大气中NH3可转化为现代大气中的______和______.

单项选择题