Now satellites are 36 to forecast（预报）the weather. They are in space, and they can 37 any part of the world. The satellites take pictures of the atmosphere（大气），38 this is where the weather forms（形成）. They send these 39 to the weather stations. So meteorologists（气象学家）can see the weather of any part of the world. From the pictures, the scientists can often say 40 the weather will change.

Today, nearly five hundred weather stations in sixty countries receive satellite pictures. When they receive new pictures, the meteorologists compare them with earlier 41 . Perhaps they may find that the clouds have changed during the last few hours. This may mean that the 42 on the ground may soon change, too. In their next weather forecast, the meteorologists can say this.

So the weather satellites are a great 43 to the meteorologists. 44 __satellites were invented, the scientists could forecast the weather for about 24 or 48 hours. Now they can make good forecasts for three or five days. Soon, perhaps, they may 45 forecast the weather for a week or more ahead（提前）.

36.________________

A. help B. to help C. helped D. helping