对于有电流通过的导线，由于发热而引起的温升超过其允许的最高温升值时会使导线的绝缘材料

Imagine the situation. You are driving in a village or on a mountain. You have no idea where you are. You passed the last house two hours ago. Then your car doesn’t work. It is night and it is cold. You have no mobile phone. What do you do? Well, next time take a GPS with you. This invention may be able to help you. It is used for finding your position(位置) with the help of satellites (卫星). A GPS can’t start your car, but at least you will know where you are.

GPS, which means Global Positioning System(全球定位系统), is a small radio receiver. It looks like a mobile phone. You can hold it in your hand, or put in your pocket. It is sometimes put into a watch or a telephone. We also find a GPS in cars, planes, or boats. Some of them have electronic maps, so you know where you are. For example, in a city they can tell you the name of the street.

There are three parts to GPS. The first part is the receiver. You can hold it in your hand, or have it fixed into your car, plane, etc. The second part is a group of satellites going around the Earth. The receiver communicates with at least four of the satellites and calculates its position. The third part of the system is a network of ground stations all over the world. They control (控制) the satellites and make sure they are working well.

Some people think that in the future the GPS will be as common as the mobile. They are becoming better and cheaper. There are also new uses for the GPS. Perhaps they will become like watches. Everyone will have one and you will never be lost again.

小题1:According to the passage, with the help of the GPS, people __________.

A．can’t be lost in a new city

B．can’t find their way in different countries

C．can learn about the culture of an unknown place

D．can spend the least time getting to another place小题2:We can learn from the passage that ____________.

A．there are three parts to the GPS

B．a GPS can’t be put into a watch

C．a GPS can help you start your car

D．the GPS are becoming more and more expensive小题3:The underlined word “They ” in paragraph 3 means “____________”.

A．Receivers

B．GPS

C．Satellites

D．Ground stations小题4:What can we infer(推断) from the passage?

A．All GPS devices have electronic maps.

B．People in many countries will use the GPS for free.

C．The receiver of the GPS communicates with at least five of the satellites.

D．The GPS will become more and more common in everyday life.

下列离子方程式表达正确的是

A．碘化亚铁溶液中通入少量氯气：Cl₂+2Fe²⁺=2Fe³⁺+2Cl^—

B．向1mol/L 0.1L的明矾溶液中加入0.5mol/L 0.2L的Ba(OH)₂溶液：

2Al³⁺+3SO₄^2—+ 3Ba²⁺+6OH^—=2Al(OH)₃↓+3BaSO₄↓

C．将蛋壳浸泡到醋酸中：CO₃^2—+2CH₃COOH=2CH₃COO^—+ CO₂↑+H₂O

D．将过氧化钠与水反应：2O₂^2—+2H₂O=O₂+4OH^—

细小的火山灰中含有二氧化硅，这种化合物的熔点是1100摄氏度。而目前大部分飞机的涡轮发动机工作温度为1400摄氏度，一旦火山灰被吸入引擎的内部，二氧化硅熔化后就会吸附在涡轮叶片和涡轮导向叶片上，导致灾难性后果。1982年，两架飞机曾经从印度尼西亚西爪哇省加隆贡火山喷发的火山灰中穿过，两架飞机的八个引擎全部停转，在从11000米高空滑翔至400米高度后才重新启动得以紧急迫降。
这段文字主要介绍( )。

A．火山灰对飞机飞行有严重影响
B．二氧化硅是火山灰的主要成分
C．降温能使飞机有效避免火山灰的危害
D．历史上火山喷发曾险些导致飞行事故

职业技能鉴定是按照国家规定的职业标准，通过政府授权的考核鉴定机构对劳动者的专业知识和技能水平进行客观、公正、科学规范地评价与认证的活动。

单线区段线桥工区应配备的停车信号牌、减速信号牌、减速地点标的数量为（）。

A、2个

B、4个

C、6个

D、8个