题目

听材料，回答问题。 （1） How long has the speaker lived in a big city? A . One year. B . Ten years. C . Eighteen years. （2） What is the speaker's opinion on public transport? A . It's comfortable. B . It's time-saving. C . It's cheap. （3） What is good about living in a small town? A . It's safer. B . It's healthier. C . It's more convenient. （4） What kind of life do the speakers seem to like most? A . Busy. B . Colorful. C . Quiet.科研人员乘气球进行科学考察.气球、座舱、压舱物和科研人员的总质量为985kg.气球在空中停留一段时间后，发现气球漏气而下降，及时堵住.堵住时气球下降速度为1m/s，且做匀加速运动，10s内下降了35m. 为使气球再次上升，立即向舱外缓慢抛出一定的压舱物.此后经2分钟气球停止下降而开始上升，若空气阻力和泄漏气体的质量均可忽略，重力加速度g=9.80m/s2，求抛掉的压舱物的质量．