用括号中所给词的适当形式填空

某人设计一项单人游戏，规则如下：先将一棋子放在如图所示正方形ABCD（边长为3个单位）的顶点A处，然后通过掷骰子来确定棋子沿正方形的边按逆时针方向行走的单位，如果掷出的点数为i（i=1，2，…6），则棋子就按逆时针方向行走i个单位，一直循环下去．则某人抛掷三次骰子后棋子恰好又回到点A处的所有不同走法共有（　　）

    I went hiking to a mountain with my friends last summer． It was a good trip at the beginning but something unexpected happened on the half way．

    One of my friends, Mike, suddenly felt a terrible pain in his stomach and he couldn't move any further． Nobody knew what to do． One girl tried to call her mum with her mobile phone but there was no signal in the mountain area． Luckily I brought medicine with me． After Mike took some, he felt much better． We walked on, and then we all enjoyed ourselves on the top of the mountain.

某同学利用右图装置测定空气中氧气的含量，红磷燃烧后恢复到室温，打开弹簧夹发现进入广口瓶的液体液面高度超过广口瓶容积的1/5。造成这一现象的原因可能是（）

被列宁称为“世界上第一次群众性，政治性的无产阶级革命运动”的是（  ）