问题 单项选择题

通过路由算法,为分组通过通信子网选择最适当的路径是OSI模型中______的任务。

A.数据链路层

B.物理层

C.传输层

D.网络层

答案

参考答案:D

解析: 本题考查OSI标准7层模型的概念。网络层通过路由算法为分组选择最佳路径,它要实现路由选择、拥塞控制与网络互连等功能。A) 数据链路层是通过差错控制和流量控制,使有差错的物理线路变成无差错的数据链路;B) 物理层是利用物理传输介质为数据链路层提供物理连接;C) 传输层的主要任务是向用户提供可靠的端到端服务,透明地传送报文。

单项选择题
阅读理解

NEW YORK (Reuters Health)--Two years after New York City declared war on artificial trans fats(人造反式脂肪酸), nearly all city restaurants had successfully cut the fats from their menus, health officials reported Monday.

In December 2006, the city’s Board of Health decided to launch a gradual trans-fat phase-out (逐步淘汰)from all licensed eating establishments--including restaurants, school cafeterias and street vending spots. Then many cities like Washington, San Francisco and Philadelphia, reflected it actively.

By November 2008, more than 98 percent of city restaurants had stopped using artificial trans fats for cooking, frying and baking, researchers with the city’s health department report in the Annals of Internal Medicine.

Trans fats have become notorious because they not only raise so-called “bad” LDL cholesterol (胆固醇), as the fats in animal products do, but also lower levels of so-called “good”HDL cholesterol.

While some meats and dairy products naturally contain trans fat, most trans fats in people’s diet are artificial; they are formed when manufacturers add hydrogen to vegetable oil to make it become solid. These so-called partially hydrogenated oils were main products in foods, like crackers, cookies and pastries, and widely used by restaurants in cooking, frying and baking.

When the restriction was first adopted, the researchers note, some critics claimed it was an Orwellian measure, while others worried that restaurants would have a tough time finding suitable trans-fat replacements.                                                     

However, the transition has been smooth, Angell’s team writes, declaring that trans-fat restriction “is now a largely unnoticed part of New York City life.”

Ridding the food supply of trans fats, the researchers write, could potentially improve the cholesterol levels of millions of people.

1. In which city the local health department first decide to stop artificial trans fats?

A. Washington.    B. San Francisco.     C. Philadelphia.      D. New York.

2. We can learn from the third paragraph that ________.

A. in the city most people still use artificial trans fats

B. only a few restaurants still use trans fats and the decision win most people’s support

C. the city’s decision proves to be useless

D. many people think using artificial trans fats is not so bad

3. The underlined word “notorious” in the fourth paragraph means ________.

A. having a very bad reputation          B. having a very good reputation

C. nutritious                         D. delicious

4. What is the main idea of the passage?

A. New York restaurants are nearly all trans-fat-free (无……有)

B. None of the restaurants in the U.S can use trans fats.

C. Most of the restaurants still use trans fats once in a while.

D. Trans fats are bad for health.