In many stories on TV and in science fiction，humans can travel to stars far away．But so far，people have only been able to get to th moon．

What if a person wants to get to a star far away？it would take a lifetime to travel．People should have to move at least at the speed（速度）of light．But in fact，nothing can move faster than light．

Light travels more than 186，000miles a second（秒），or about 11million miles a minute．In one year，light travels about 6trillion（6，000，000，000，000）miles．That great distance is called a light-year（光年）．It is used to measure（测量）distance in space．

Strange things happen to an object（物体）when it moves very fast．If an object moves at 86% of the speed of light，It will be twice as heavy as it is at rest．A stick appears shorter．A clock runs more slowly．A person would not age so fast in space as on the earth．

Alpha Centauri is the closest star to the sun．It is over four light-years away．So if a human traveled at the speed of light，it would take him nine years to go to Alpha Centauri and come back．

根据短文内容，选择最佳答案．

66．About the speed of light，which of the following is true？___

A．Light travels about 11million miles a second．

B．Light travels more than 186，000miles a minute．

C．Light travels about 11million miles an hour．

D．Light travels about 6trillion miles a year．

67．So far the farthest place humans have got to is___．

A．Alpha Centauri

B．the sun

C．the moon

D．the earth

68．The underlined word"age"means___．

A．老年

B．变老

C．年龄

D．时代

69．It would take a person___ to get to Alpha Centauri at the speed of light．

A．more than 4years

B．less than 2years

C．about 9years

D．about 11years

70．What's the best title（标题）of this article？___

A．The distance between the sun and other stars．

B．How to travel to Alpha Centauri？