【正文】 to dial instructions about his destination into the puter will calculate the best route, and reserve space for the car all the way to the correct exit from the driver will then be free to relax and wait for the buzzer（蜂鳴器）that will warn him of his ing is estimated that an automated highway will be able to handle 10,000 vehicles per hour, pared with the 1,500 to 2,000 vehicles that can be carried by a presentday ，在第三段，即文章中間才給出主題句，講解決城市交通堵塞的一個(gè)方法是自動(dòng)高速公路系統(tǒng)。后面兩段具體介紹自動(dòng)高速公路系統(tǒng)是如何工作的。請讀下面的文章并且找到主題句，做出主旨題。The biggest safety threat facing airlines today may not be a terrorist with a gun, but the man with the portable puter in business the last 15 years, pilots have reported well over 100 incidents that could have been caused by electromagnetic source of this interference remains unconfirmed, but increasingly, experts are pointing the blame at portable electronic devices such as portable puters, radio and cassette players and mobile , an organization which advises the aviation（航空）industry, has remended that all airlines ban（禁止）such devices from being used during “critical” stages of flight, particularly takeoff and experts have gone further, calling for a total ban during all , rules on using these devices are left up to individual although some airlines prohibit passengers from using such equipment during takeoff and landing, most are reluctant to enforce a total ban, given that many passengers want to work during difficulty is predicting how electromagnetic fields might affect an aircraft’s know that portable devices emit radiation which affects those wavelengths which aircraft use for navigation and , because they have not been able to reproduce these effects in a laboratory, they have no way of knowing whether the interference might be dangerous or fact that aircraft may be vulnerable（易受損的）to interference raises the risk that terrorists may use radio system in order to damage navigation worrying, though, is the passenger who can’t hear the instructions to turn off his radio because the music’s too : The passage is mainly )a new regulation for all airlinesB)the defects of electronic devicesC)a possible cause of aircraft crashesD)effective safety measures for air flight【答案解析】C。從每段的第一句話可知文章講述電磁干擾對于飛機(jī)安全的影響和飛行事故的可能原因。Believe it or not, optical illusion（錯(cuò)覺）can cut highway is a case in has reduced automobile crashes on some roads by nearly 75 percent using a simple optical stripes, called chevrons（人字形）painted on the roads make drivers think that they are driving faster than they really are, and thus drivers slow the American Association Foundation for Traffic Safety in Washington planning to repeat Japan’s next year, the foundation will paint chevrons and other patterns of stripes on selected roads around the country to test how well the patterns reduce highway speed plays a major role in as much as one fifth of all fatal traffic accidents, according to the help reduce those accidents, the foundation will conduct its tests in areas where speedrelated hazards are the greatest—curves, exit slopes, traffic circles, and studies suggest that straight, horizontal bars painted acr