合作作品不可以分割使用的，其著作权由各合作作者共同享有，通过协商一致行使；不能协商一

金属钛对人体无毒且惰性，能与肌肉和骨骼生长在一起，有“生物金属”之称．下列有关₂₂⁴⁸Ti和₂₂⁵⁰Ti的说法中正确的是（　　）

A．₂₂⁴⁸Ti和₂₂⁵⁰Ti在周期表中位置相同，都在第4周期

B．₂₂⁴⁸Ti与₂₂⁵⁰Ti为同一核素

C．₂₂⁴⁸Ti和₂₂⁵⁰Ti原子中均含有22个中子

D．分别由₂₂⁴⁸Ti和₂₂⁵⁰Ti组成的金属钛单质互称为同分异构体

对照ISO/OSI参考模型各个层中的网络安全服务，在传输层主要解决进程到进程间的加密，最常见的传输层安全技术有 (1) ；为了将低层安全服务进行抽象和屏蔽，最有效的一类做法是可以在传输层和应用层之间建立中间件层次实现通用的安全服务功能，通过定义统一的安全服务接口向应用层提供 (2) 安全服务。在数据链路层，可以采用 (3) 进行链路加密；在网络层可以采用 (4) 来处理信息内外网络边界流动和建立透明的安全加密信道；在物理层可以采用 (5) 加强通信线路的安全。

4（）

A．防窃听技术

B．防火墙技术

C．防病毒技术

D．IPsec

阅读理解。

     Do I really need a helmet just to ride to class?

     First, ask your physics professor what can happen to a head dropped from the normal height where you

ride, say about 5 feet up, when it hits the walkway? He will tell you about the forces the head can experience

from that drop height. Bike helmets are tested in a two-meter drop, a little higher, but that five feet is all the

force you need to mess up your brain. You don't need forward speed at all, although it can make it worse.

     Then think about accidents that happen when you ride on campus. Have you had near-collisions (碰撞)

or actual collisions with pedestrians as the students change class? Do you ever hurry to get to class and take

little chances? Have you ever seen a patch of ice or sand on a campus sidewalk? We would bet that you know

more risk factors than we do.

     And what do the statistics say? There are 800 people killed on bikes, and a half million, more or less

injured, in the US every year. Nobody keeps track of how many of those were on a campus. But we do know

that you are making a major investment in yourself for a lifetime of good returns. People with head injuries

can remember how much more they were able to do mentally before the crash, and that hurts long after other

parts heal (愈合). The effects can last forever. At your age you are just beginning to realize how much

pleasure in life comes from being experienced, smart and educated. You don't want to take a chance with that.

It means a lot to you.

     Helmets are cheap at Wal-Mart or Target, and the cheap ones work fine if you fit them carefully. It really

won't mess up your hair much in a short ride. Give it a try. 

1. The aim of this text is probably______.

A. to introduce a way to protect one's head

B. to remind students to wear helmets while riding

C. to persuade students to buy more helmets at Wal-Mart

D. to warn students against bicycle riding because of danger

2. Helmets are necessary for bicycle riders on campus because _____.

A. they will meet with an accident sooner or later

B. the brain will be protected during an accident

C. their hair will not be messed up in a short ride

D. they will have to fight against the students from other classes

3. In paragraph three, the writer mainly wants to tell us that _____.

A. riding bicycles is too dangerous

B. the traffic on the campus is often out of order

C. the number of bicycles on campus should be limited

D. it is difficult to avoid accidents while riding bicycles on campus

4. The "major investment" refers to the money for _____.

A. a safer bike

B. bike accidents

C. a helmet

D. a campus insurance

5. This passage would probably appear in the part of ______ on a website.

A. Science

B. News

C. Education

D. gym

干式变压器装设的保护有（）。

A、电流速断；

B、瓦斯保护；

C、过流保护；

D、压力释放。

通常把软件分为系统软件和应用软件两大类，下列选项中哪个不是应用软件

A．财务管理系统软件

B．数据库管理系统软件

C．报表处理软件

D．绘图软件