单选题 .  In some areas of the world the weather is very     1    and this fact plays an important part in the daily lives of the people.     2    they are farmers, fishermen, or sailors, for instance, they     3    know about these changes ahead of time. Space scientists and airplane pilots     4    need weather     5    .
        6    earliest time, men have     7    the sky, tile wind, and the atmosphere, as well as a variety of other weather signs, in order to make weather     8    . But often their weather predictions have not been accurate. Now there are government bureaus in many places that     9    weather conditions very carefully. They use a lot of scientific     10    to help them make their forecasts. For instance, they have instruments to     11    speed and direction of the wind. Thus they can     12    the path of a storm. They have special balloons, ships, and airplanes to help them     13    their accuracy, and they make use of radar, satellites and computers to gather     14    information.
    Today when a plane     15    from an airport, the pilot can know what kind of weather to expect     16    he reaches his destination(目的地). If there is     17    rain or snow in the mountains, a weather bureau can predict the day and     18    the hour that a river may overflow(使涨满) its banks many miles away. When a storm is moving in a     19    path, the people in that area can learn of it ahead of time and     20    it.1.