用化学用语填空：
（1）三个氢原子____  

（2）两个五氧化二氮分子____
（3）3个氢氧根离子____ 

（4）氧化镁中镁元素为+2价____

如图所示，轻质弹簧一端固定，另一端与质量为m、套在粗糙竖直固定杆A处的圆环相连，弹簧水平且处于原长．圆环从A处由静止释放后，经过B处速度最大，到达C处（AC=h）时速度减为零．若在此时给圆环一个竖直向上的速度v，它恰好能回到A点．弹簧始终在弹性限度内，重力加速度为g，则圆环（   ）

选词填空。

    My favourite TV programme is a reality show called Survivor(《幸存者》). It isn't on TV at the moment ____  it was on last year.

    In the show, two teams of people are taken to a(an) ____ . All of them have to sleep ____  because there aren't any houses or hotels. They usually choose ____ really useful like a tooth brush since they can only ____ one thing with them. The people also have to find food and they spend a lot of time fishing and collecting fruits from the ____ . Every week one person has to____ . At the end, there are only two people on the island and one of them is chosen ____ the winner.

    I really like Survivor because it's very ____  and the people have to do things like hunting for food. I really ____  myself when I watch it. I don't want to be on the show, however, I like 1iving in a house!