题目

-It's said that shopping on line is safe．-____．You'd better be careful．A. I agree B. That depends C. I think so D. No problem 答案：【答案】B【解析】句意：——据说网上购物是安全的．——那要看情况了，你最好小心点．考查情景交际。A.I agree我同意；B. That depends要看情况而定；C. I think so我认为是这样；D. No problem没问题．从You'd better be careful，判断前面说的是That depends要看情况而定．故选：B．航模兴趣小组设计出一架遥控飞行器，其质量m =2㎏，动力系统提供的恒定升力F ="28" N。试飞时，飞行器从地面由静止开始竖直上升。设飞行器飞行时所受的阻力大小不变，g取10m/s2。（1）第一次试飞，飞行器飞行t1 =" 8" s 时到达高度H =" 64" m。求飞行器所阻力f的大小；（2）第二次试飞，飞行器飞行t2 =" 6" s 时遥控器出现故障，飞行器立即失去升力。求飞行器能达到的最大高度h