根据短文内容，用方框中所给单词的适当形式填空，每词限用一次。

Have you heard of “car sharing”? The idea of “car sharing” is becoming more  小题1: in Europe and the USA. “Car sharing” is that people drive together in the same car to work, instead of  小题2:  their own cars.

On average , we drive our cars only one hour every day. The rest of the time we  小题3: park our cars in parking places and we have to  小题4: too much money in parking our cars in the city. To save money and help the environment, people  小题5: to share cars several years ago. ”Car sharing” is a good way for us to save money, time, and help the environment at the same time. What a great idea!

正常人肺动脉频谱多普勒为

A．正向双峰窄带波形

B．上升支陡峭，下降支圆的不对称三角形

C．上升支与下降支对称的负向频谱

D．呈楔形负向血流频谱

E．加速支陡直的频谱曲线