great-step-forward什么意思?原句It was a great-step-forward for man.
原段Bows and arrows,are one of man's oldest weapons.They gave early man an effective weapon to kill his enemies.The ordinary bow or short bow was used by early all early people.This bow bad limited power and short range.However,man overcame these faults by learning to track his targets at a close range.The long bow was most likely discovered when someone found out that a five-foot piece of wood made a better bow than a three-foot piece.Hundreds of thousands of these bows were made and used for three hundred years.However,not one is known to survive today.We believe that a force of about one hundred pounds was needs to pull the string all the way back on a long bow.For a long time the bow was just a bent stick and string.In fact,more changes have taken place in a bow in the past 25 years than in the last 7 centuries.Today,bow is forceful.It is as exact as a gun.In addition,it requires little strength to draw the string.Modern bows also have precise aiming devices.In indoor contests,perfect scores from 40 yard are common.The invention of the bows itself ranks with discovery of fire and the wheel.It was a great-step-forward for man.