题目

These days we hear a lot about how air pollution is changing temperatures on the earth. New evidence from a mountaintop in China now suggests that pollution can also change the amount of rain and snow that falls in some places.        Usually, more rain falls in mountainous places than in flat areas upwind from the mountains. That’s because air can hold a lot of water. When wind blows wet air up a mountainside, the air gets colder. This temperature change often forces water to fall as rain or snow.        In recent years, however, many mountainous areas in the western United Stat物体以15m/s速度竖直向上抛出，整个运动过程加速度大小为10m/s2，方向竖直向下，则当速度大小变为10m/s时经历时间可以是（空气阻力不计，g=10m/s2）（ ）A．0．5s B．1s C．1．5s D．2．5s