搜题请搜索小程序“爱下问搜题”
问题 选择题

科学家发现C60后，近年又合成了许多球形分子（富勒烯），如C50、C70、C120、C540等，它

们互称为                                                                                                 （   ）

A．同系物

B．同分异构体

C．同素异形体

D．同位素

答案

C

C50、C70、C120、C540等都是C的不同单质，它们应互称为同素异形体，故应选C。

问答题 简答题

简述归档文件整理的工作步骤。
查看答案
阅读理解

Some people don't believe that driving more slowly can save lives．But the truth is that driving more slowly can help a person to avoid serious accidents．

The above chart（表格） shows the distance that it takes to stop a car at a given speed．The distance is measured in feet．The shaded area（阴影部分） shows the driver's thinking distance．That's the distance it takes for the driver to react to a danger that he sees．The white area shows the car's braking distance．That's the distance it takes for the car to stop once the brakes（闸、刹车） are used．The number at the top of each bar shows the total number of feet that it takes to stop the car

小题1:According to the chart, what is the total number of feet needed to stop a car that is traveling at 50 miles per hour?

A．55．

B．73．

C．128．

D．183．小题2:What is the braking distance for a car that is travelling at 60 miles per hour?

A．66 feet．

B．119 feet．

C．185 feet．

D．251 feet．小题3:Which of the following statements about braking and speed is true?

A．The braking distance is what it takes for the driver to react to a danger that he sees．

B．The speed of a car has a direct effect on the distance needed to stop the car．

C．The braking distance increases only when a driver drives faster than 50 miles per hour.

D．Driving slowly can help a person to avoid all accidents
查看答案