The computer works with an antenna (天線) that takes signals from no fewer than three or the24, global positioning system (GPS) satellites. By measuring the time required for a signal totravel between the satellites and the antenna. the car's location can be pinned down within l00meters.

　　The satellite signals. along with inputs on speed from a wheel-speed sensor and direction froma meter, determine the car’s position even as it moves. This information is combined with amap database. Streets, landmarks and points of interest are included.

　　Most systems are basically identical. The differences come in hardware-the way the computeraccepts the driver's request for directions and the way it presents the driving instructions. Onmost systems, a driver enters a desired address, motorway junction or point of interest via atouch screen or disc. But the Lexusscreen goes a step further: you can point to any spot onthe map screen and get directions to it.

　　BMW's system offers a set of cross hairs(瞄準器上的的十字紋)that can be moved across themap (you have several choices of map scale) to pick a point you'd like to get to. Audi's screencan be switched to TV reception.

　　Even the voices that recite the directions can differ, with better systems like BMW's andLexus's having awider vocabulary. The instructions are available in French. German, Spanish,Dutch and Italian, as well asEnglish. The driver can also choose parameters for determining theroute: fastest, shortest or no freeways(高速公路), for example.

　　現在大多數汽車制造商出售的導航電腦價值都在2000美元或以上，因此它們大多用于一些豪華車內，如凌志，寶馬和奧迪，也是不足為奇的事。[1]但它是一種發(fā)展中的技術——這意味著價格最終將下降——市場看來定將擴大。

　　即使就當前的價格而吉，導航電腦也足以令人動心。它通過精確的轉彎方向提示指引你在大多數重要城市里由此地去彼地。這些指示可以模擬清晰的真人發(fā)音，并書寫在駕駛者面前的屏幕上。

　　該電腦通過一根天線工作。這根無線至少能夠接收到24家全球定位衛(wèi)星中的3家。通過計算衛(wèi)星與天線之間信號傳播所需的時間，汽車的位置可被確定在lOO米的誤差范圍之內。

　　[4]衛(wèi)星信號，連同車速傳感器提供的車速數據和定向儀提供的方向一起確定出車子的位置，哪怕它處于移動當中。這些信息同一個地圖數據庫相結合，街道、路標或名勝之地都被包括在該數據庫之中。

　　[3]/[5]大多數導航系統基本都是相同的。區(qū)別之處在于硬件的不同，即電腦接受駕駛者詢問方向的指令，以及它提供指示的方式不同。[2]在多數系統內，駕駛者通過觸摸屏或光盤輸入某個目的地地址，高速公路的交匯口，或名勝之處。但是凌志車的屏幕則更勝一籌：你能夠指向屏幕地圖的任何一點并獲得到達該地點的指示。

　　根據德國寶馬的系統設計，地圖上有一個可以移動的瞄準十字紋(有幾種地圖比例供選擇)。你想去哪里，就可以選定那里。而奧迪車的屏幕可以轉換為電視接受器。

　　像寶馬和凌志這樣的車，其更為出色的定位系統所儲存的詞匯量更大，甚至其復述指令的聲音也可以不同。這些指令除可以英語發(fā)音外，還可以使用法語、德語、西班牙語、荷蘭語和意大利語發(fā)音。駕駛者還可以通過設置參數來決定路線，比如說最快、最短、或不走高速公路的路線。

　　1. We learn from the passage. that navigationcomputers______________.

　　A) will greatly promote sales of automobiles

　　B) may help solve potential traffic problems

　　C) are likely to be accepted by more drivers

　　D) will soon be viewed as a symbol of luxury

　　2. With a navigation computer, a driver will easily find the best route to hisdestination________.

　　A) by inputting the exact address

　　B) by indicating the location of bis car

　　C) by checking his computer database

　　D) by giving vocal orders to the computer

　　3. Despite their varied designs, navigation computers used incars___________________.

　　A) are more or leas the same price

　　B) provide directions in much the same way

　　C) work on more or less the same principles

　　D) receive instructions from the same satellites

　　4. The navigation computer functions__________________.

　　A) by means of a direction finder and a speed detector

　　B) basically on satellite signals and a map database

　　C) mainly through the reception of turn-by-tum directions

　　D) by using a screen to display satellite signals

　　5. The navigation systems in cars like Lexus. BMW and Audi are mentioned toshow__________.

　　A) the immaturity of the new technology

　　B) the superiority of the global positioning system

　　C) the cause of price fluctuations in car equipment

　　D) the different ways of providing guidance to the driver