[单选题]挂线时,当连接金具接近挂线点时应( )牵引,然后作业人员方可从安全位置到挂线点操作。
A. 停止
B. 减速
C. 加速
D. 匀速

Many of the most damaging and life threatening types of weather--torrential rains, severe thunderstorms, and tornadoes--begin quickly, strike suddenly, and disappear rapidly, destroying small regions while leaving neighboring areas untouched. Such event as a tornado struck the northeastern section of Edmonton, Alberta, in July 1987. Total damages from the tornado exceeded $250 million, the highest ever for any Canadian storm.
Conventional computer models Of the atmosphere have limited value in predicting short lived local storms like the Edmonton tornado, because the available weather data are generally not detailed enough to allow computers to study carefully the subtle atmospheric changes that come before these storms. In most nations, for example, weather-balloon observations are taken just once every twelve hours at locations typically separated by hundreds of miles. With such limited data, conventional forecasting models do a much better