一组正方形按如图所示的方式放置，其中顶点B₁在y轴上，顶点C₁，E₁，E₂，C₂，E₃，E₄，C₃……在x轴上，已知正方形A₁B₁C₁D₁的边长为1，∠B₁C₁O＝60°，B₁C₁∥B₂C₂∥B₃C₃……则正方形A₂₀₁₇B₂₀₁₇C₂₀₁₇D₂₀₁₇的边长是____；

沿河设城主要是因为（   ）
①河流为城市提供生活用水和工业用水
②河流为城市运送废水，加速净化
③河流为城市提供便利的水运条件
④河流为城市增加一条风景线，并有利于防卫

完形填空

        It might have been a really bad stressful day, feeling trapped inside by the cold and snow which surrounded us.My husband got dressed and 1that he was going outside to build a giant snowman.

       At first he stood alone，2massive amounts of snow.Soon after a neighbor joined in.Then we reluctantly put on our snow gear and3outside.It wasn't long4we were smiling and enjoying the 5of snow that Mother Nature had provided.Others came to our yard one by one to give a  6in the making of our giant snowman.

       In the end we all stood back and7at what we had created.He was eleven feet high, twenty­five feet around at the base and 8with many household items supplied by various9．People drove by and smiled.Some even stopped just to enjoy his10．

       With the passing of time, the spring made its 11back into our yard and the snowman changed form12．In a final effort to save what we created for just a little bit 13，somebody stopped by and changed the snowman's 14to look like a rabbit.As I prepared for the start of another week, I decided to 15my e­mail before going to bed.I found a (an) 16message that contained the subject line：17the snowman.

       The e­mail said：your neighbor looks on in disbelief！Now you people are relishing(享受)the sounds and smells, along with18of spring.But I am sure people will never forget the 19energy displayed in Mr.Snowman.You and your family keep it up, as this is what the world needs now.More power to you and your loved ones, keep  20with the world around!

       Perhaps it was more than a snowman we built that day.The message seems clear.Our environments will turn out to be what we make of them.The possibilities are endless and the choice is ours.

Notes：

①reluctantly adv.勉强地，不情愿地　②disbelief n．不相信

阅读下面短文，回答问题。

     （甲）有一件小事，我不知道还值不值得提它，但回想起来，在那时却占据过我的心灵。我父亲那时候在军阀部队里，好几年没有回来，我跟母亲非常牵挂他，不知道他的死活。我的母亲常常站在一张褪了色的神像面前焚起香来，把两个有象征记号的字条卷着埋在香炉里，然后磕了头，抽出一个卜问吉凶。我虽不像母亲那样，也略略懂了些事。可是在孩子群中，我的那些小“反对派”们，常在我的耳边猛喊：“哎哟哟，你爹回不来了哟，他吃了炮子儿！”那时的我，真好像死了父亲似的那么悲伤。这时候蔡老师援助了我，批评了我的“反对派”们，还写了一封信劝慰我，说我是“心清如水的学生”。一个老师排除孩子世界的一件小小的纠纷，是多么平常；可是回想起来，那时候我却觉得是给了我莫大的支持！在一个孩子的眼睛里，他的老师是多么慈爱，多么公平，多么伟大的人啊。

     （乙）但不知怎地，我总还时时记起他，在我所认识的老师之中，他是最使我感激，给我鼓励的一个。有时我常常想：他的对于我的热心的希望，不倦的教诲；小而言之，是为中国，就是希望中国有新的医学；大而言之，是为学术，就是希望新的医学传到中国去。他的性格，在我的眼里和心里是伟大的，虽然他的姓名并不为许多人知道。