M7120型磨床的液压泵电动机和砂轮升降电动机的正反转控制可采用（）来实现。 A.点

下列各组词语中加点字的读音，完全相同的一组是（     ）

A．福祉胼胝扺掌而谈咫尺天涯

B．抚恤怃然惊魂甫定果脯蜜饯

C．差劲　　惊诧　　　姹紫嫣红　　叱咤风云

D．卓越着落擢发难数斫伐树木

若x⁴-16分解因式正确的是[ ]

A．（x²+4）（x²﹣4）

B．（x²+4）（x²+4）

C．（x²+2x+4）（x²﹣2x+4）

D．（x²+4）（x+2）（x﹣2）

在竖直平面内，由光滑斜面和光滑半圆形轨道分别与粗糙水平面相切连接而成的轨道如图所示，半圆形轨道的半径为R=0.4m，质量为m=0.8kg可视为质点的小物块从斜面上距水平面高为h处的A点由静止开始下滑，物块通过轨道连接处的B、C点时，无机械能损失．运动到圆轨道最低点C处时对轨道的压力为N=40N，水平轨道BC长L=0.9m，滑块与水平面间的动摩擦因数为（μ=0.5，g取10m/s²．求：

（1）A点距水平面的高度h；

（2）小物块第一次由B点到C点运动的时间；

（3）小物块能否通过圆形轨道的最高点D．

在近髓端和近表面牙本质小管的数目比约为

A．1:1

B．1:4

C．4:1

D．1:8

E．8:1

When Melissa Mahan and her husband visited the Netherlands, they felt imprisoned by their tour bus. It forced them to see the city according to a particular route and specific schedule--but going off on their own meant missing out on the information provided by the guide. On their return home to San Diego, California, they started a new company called Tour Coupes. Now, when tourists in San Diego rent one of their small, brightly coloured three-wheeled vehicles, they are treated to a narration over the stereo system about the places they pass, triggered by Global Positioning System (GPS) satellite technology.

This is just one example of how GPS is being used to provide new services to tourists. "What we really have here is a technology that allows people to forget about the technology," says Jim Carrier of IntelliTours, a GPS tourism firm which began offering a similar service over a year ago in Montgomery, Alabama. The city is packed with sites associated with two important chapters in American history, the civil war of the 1860s and the civil-rights movement a century later. Montgomery has a 120-year-old trolley system, called the Lightning Route, which circulates around the downtown area and is mainly used by tourists. On the Lightning Route trolleys, GPS-triggered audio clips point out historical hotspots.

Other firms, such as CityShow in New York and GPS Tours Canada in Banff, Canada, offer hand-held GPS receivers that play audio clips for listening to while walking or driving. In South Africa, Europcar, a car-rental firm, offers a device called the Xplorer. As well as providing commentary on 2 000 points of interest, it can also warn drivers if they exceed the local speed limit.

If such services prove popular, the use of dedicated audio-guide devices could give way to a different approach. A growing number of mobile phones have built-in GPS or can determine their locations using other technologies. Information for tourists delivered via phones could be updated in real time and could contain advertisements. "Location-based services", such as the ability to call up a list of nearby banks or pizzerias, have been talked about for years but have never taken off. But aiming such services at tourists makes sense--since people are more likely to want information when in an unfamiliar place. It could give mobile roaming a whole new meaning.

The word "chapter" ( Line 4, Paragraph 2) denotes （）

A. event

B. a local branch of an organization

C. division of a book

D. period of time