was designed many years ago，with a goal in mind：transmitting the human voice in a more-or-less recognizable form．

It can be learned from the passage that about four billion years ago ______.

The output of our factory is now twice ______________ it was three years ago.

__________different life today is__________ what it was 15 years ago.

It was about 600 years ago （） the first clockwith a face and an hour hand was made.

Our factory is much more productive now. This year’s production is five times as much （） it was ten years ago.

It’s（）to stow optional cargo in the lower hold．You’d better give it block stowage in the tweendecks，then it can be easily discharged either at Shanghai，or Dalian or Tianjin.

练习17　　Five hundred years ago, news of important happenings—battles lost and won, kings or rulers overthrown or killed—took months and even years to travel from one country to another. The news passed by word of mouth and was never accurate. Today we can read in our newspapers of important events that occur in faraway countries on the same day they happen.

Believe it or not, when first (introduce) ____ to Europe, tomato was thought to be poisonous.

 ______ twice a year, whether it is a car or a bus or a truck, is the rule that every driver must obey in this city.

Scientists say it may be five or six years _____ this medicine is tested on human beings.

Hundreds of years ago there was a war between _____.