已知数列{a_n}的前n项和为S_n，且满足a₁= $\frac{1}{2}$ ，2S_n﹣S_nS_n﹣1=1（n≥2）．

飞机由俯冲转为拉起的一段轨迹可看作一段圆弧，如图所示，飞机做俯冲拉起运动时，在最低点附近做半径为r＝180 m的圆周运动，如果飞行员质量m＝70 kg，飞机经过最低点P时的速度v＝360 km/h，则这时飞行员对座椅的压力F=____N。（g＝10 m/s²）

The place          the bridge is supposed to be built should be             the cross river traffic is the heaviest.

下列为四种遗传病的系谱图，能够排除伴性遗传的是（    ）

阅读下面对话，并根据要求完成相应任务。从所给的A、B、C、D、E选项中，选择正确的小标题。
①I am 73 years old. I often watch TV in my free time. Of all the programs, I like the news best. Through the TV, I can learn what is happening in our country and in the world. At seven every evening, I always sit in front of the TV. ____   
②I am a grandma. I like Chinese traditional opera. From Monday to Thursday, I usually turn on the TV at half past seven. The programs from CCTV7 are my best.  ____   
③I am a basketball fan. I like playing basketball very much. But I am too busy. So I have to watch it on TV. Every night, I watch the match till midnight. I am crazy about it. ____   
④I am a housewife. I do the housework all day, I'd like to watch TV at night. I like to watch soap operas such as "Palace", "Meteoric Garden" and so on.  ____   
⑤I am the only son in the family. I am in Grade One. I like cartoons best. I often watch cartoons on TV after doing the homework. ____   
A.          
B.           
C.         
D.         
E.