阅读下列材料，回答问题。 
材料一  1660年的《航海条例》，规定北美殖民地所有的输入和输出商品都要使用英国船只运输，一切商品只能运往英国。
材料二 诉诸武力的办法是由英王选择的，北美大陆已经接受了这个挑战
                                                                                                                                                                      —— 托马斯·潘恩
材料三 我们以这些殖民地的善良人民的名义和权力，谨庄严宣告：这些联合殖民地从此成为、而且名正言顺的成为自由独立的合众国，他们解除对英王的一切隶属关系，而他们与大不列颠王国的一切政治联系也应从此完全废止。
（1）根据材料一和所学知识，说明北美独立战争爆发的根本原因是什么？
（2）“挑战”开始的标志性事件是什么？ 
（3）这段材料出自什么文献？该文献发表于哪一年？

造房子时屋顶常用三角结构，从数学角度来看，是应用了____ ；而活动挂架则用了四边形的____ ．

    It's Sunday. Children don't go to school on Sundays. But Kate gets up early in the morning. “It's my birthday. I'm eight years old today.” she thinks, “Where are Dad and Mum? I want to know what they can give me for my birthday.”

    Her father and mother are not at home. They are going shopping. And now they are talking about what to buy for Kate.

—Dad: How about the doll? It looks nice. I think Kate would like the doll.

—Mom: I don't think so. She is not a little girl. I think she likes a new dress. Girls often like new dresses very much.

—Dad: But she has a few new dresses and some new blouses. Oh, I think she must be very happy to have a box of colorful pencils and some picture books. Do you think so?

— Mom: Yes. Let's go over there and buy them.