A、They are accurate and easy to pull. B、Their shooting range is 40 yards. C、They are usually used indoors. D、They took 100 years

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 as used by nearly all early people. This bow had limited power and short range. However, man overcame these faults by learning to track his targets at a close range. The long how was most likely discovered when someone found out that a five-foot piece of wood made a better bow than a three-food 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 needed 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 contest, perfect scores from 40 yards are common. The invention of the bows itself ranks with discovery of fire and the wheel. It was a great-step-forward for man.
18. Why did man have no track his target at a close range when using a short bow ?
19. What does the passage tell us about long bow?
20. What do we know about modern bows?