联锁基本原则之一是列车、调车进路上的所有道岔板动到所需的位置后，防护此进路的信号机才

美国“9•11”事件发生后，又出现炭疽热病，致死率高达25%～60%．治疗时常用环丙沙星抗生素，其化学式为C₁₇H₁₈FN₃O₃，它由______种元素组成，一个分子中含有______个原子．

选择性辐射

阅读理解。

     Tourism was not always as important as it is today．In the past only rich people could afford costly

travel to other countries．But in 1976 one common person in twenty visited a country away from home．

     More people travel today than in the past mainly because there is a growing middle class(中产阶级)

in many parts of the world．People now have more money to travel．Airplane fares at a bargain price

(特价)for tourists make travel less expensive and thus more attractive than ever before．

     One person does not travel for the same reason as another．But more people enjoy seeing countries

that are different from their own．They also travel to meet new people and try new foods．

     Tourism causes many changes in a country and in people's lives．People build new hotels and train

native men and women as tourist guides．There are new night clubs and other amusements．

International tourism is clearly a big business．

1．More people travel today than in the past mainly because ________．

A．more people get interested in traveling

B．traveling today is more popular than in the past

C．people now have extra money for travel

D．more people want to see other parts of the world with their own eyes

2．What makes travel more attractive than ever before?

A．Special telegraph lines make travel less expensive．

B．New hotels and restaurants are built now．

C．More guides are being trained for tourists．

D．Travel by plane to other countries is much cheaper today．

3．Which of the following is wrong?

A．People travel for different reasons．

B．Most people like to see foreign countries．

C．When people travel they like to make good use of the plane．

D．People like to learn from the people of other countries．

4．Which statement does this passage lead you to believe?

A．Tourism will bring no changes in people's minds．

B．Tourism causes only some changes in food and in clothing of a country．

C．Tourism causes many changes in agriculture．

D．Tourism causes obvious changes in many ways of a country．

下井、池作业人员必须经过（），懂得人工急救的基本方法，明白防护用具、照明器具和通讯器具的使用方法。

A.救护培训

B.急救培训

C.安全技术培训

D.技能培训

液流流线和迹线总是重合的。