设A （x1 ，y1 ），B （x2 ，y2）为抛物线y2=2px（p>0）上位

Some pessimistic experts feel that the automobile is bound to fall into disuse. They see a day in the not-too-distant future when all autos will be abandoned and allowed to rust. Other authorities, however, think the auto is here to stay. They hold that the car will remain a leading means of travel in the foreseeable future.

The motorcar will undoubtedly change significantly over the next 30 years. It should become smaller, safer, and more economical, and should not be powered by the gasoline engine. The car of the future should be far more pollution-free than present types.

Regardless of its power source, the auto in the future will still be the main problem in urban traffic congestion (拥挤). One proposed solution to this problem is the automated highway system.

When the auto enters the highway system, a retractable (可伸缩的) arm will drop from the auto and make contact with a rail, which is similar to those powering subway trains electrically. Once attached to the rail, the car will become electrically powered from the system, and control of the vehicle will pass to a central computer. The computer will then monitor all of the car’s movements.

The driver will use a telephone to dial instructions about his destination into the system. The computer will calculate the best mute, and reserve space for the car all the way to the correct exit from the highway. The driver will then be free to relax and wait for the buzzer (蜂鸣器) that will warn of his coming exit. It is estimated that an automated highway will be able to handle 10,000 vehicles per hour, compared with the 1,400 to 2,000 vehicles that can be carried by a present-day highway.

One significant improvement in the future car will probably be ().

A. its power source

B. its driving system

C. its monitoring system

D. its seating capacity

铸造18-8铬镍不锈钢具有良好的生物安全性和机械性能，其化学性能稳定、抗腐蚀性能良好，临床上主要用于制作下列哪一项

A．连接杆

B．正畸弓丝

C．锁槽

D．无缝冠

E．白合金片

19世纪制造的钢琴

在考虑自行车和行人通行的隧道，人行道宽度最小为（）。

A.0.5m

B.0.75m

C.1.0m

D.1.25m

何谓血压？血压受哪些因素影响？