阅读材料，完成下列要求。

材料一：由于夏、商、西周朝代的共主与各诸侯国都是作为相对独立的国际政治行为体并列存在，使得该时期的大一统主要体现在土地、民心层面，而秦统一六国则最终实现了制度层面的天下大一统。在此过程中，尽管历次朝代更迭都会出现土地及民心层面的天下分裂，但伴随着民族文化的碰撞与融合，也使得土地范围从中原地区不断向四方扩展，民心也更加凝聚到对共主的认同上，并在最终经历过春秋战国的重重洗礼之后实现了制度层面上从统一礼仪向建立秦朝中央集权体制的飞跃。

——摘编自王宣华《先秦中原文化区域“大一统”秩序观及当代价值探析》

材料二：1924年11月，孙中山在日本的演说《中国内乱之原因》中说：“说到和平统一，是我在数年前发起的主张。不过那些军阀都不赞成，所以总是不能实行这种主张。这次我到北方去，能够做成和平统一，也未可知。不过要以后真是和平统一，还是要军阀绝种；要军阀绝种，便要打破串通军阀来作恶的帝国主义。”……孙中山始终把武装斗争视为达到国家统一应采取的主要方式。为实现国家统一，孙中山一生都在不断与各派势力作斗争。在坚持武力统一的同时，孙中山从未放弃过和平统一的努力。

——摘编自王建《论孙中山的国家统一思想》

自然界中，亚硝酸盐分布广泛，没有腌制的蔬菜中也含有一定量的亚硝酸盐，下图为泡菜腌制过程中亚硝酸盐含量变化曲线，其中正确的是（   ）

函数f（x）=（a²﹣3a+3）a^x是指数函数，则a的值为（   ）

植物进行呼吸作用的主要场所是（　　）

阅读下面短文, 从短文后各题所给的四个选项(A、B、C、D)中, 选出可以填入空白处的最佳选项。
     “Paul must have been trying to carry his waste paper to garbage can and dropped a few pieces.” I1picking them up. 2later I found more pieces. No quiet sighing this time. I 3 ,“Who is throwing garbage?” No answer. Instead, I saw more bits of paper silently floating 4 from upstairs. Looking up, I saw my seven-year-old son, Paul.
     “Stop making a mess.” “It's not a mess. They're5.” “Sorry, what did you say?” I hadn't heard him clearly.
    He didn't answer me. Paul has autism (自闭症) and6answers a question, especially when he's7attentively on something else. He ran down the stairs. “Where are my other butterflies?” he asked,8around. Every time Paul 9five or more words together, my heart says a 10of thanks. But lately he seems to 11that the benefits of forming complete sentences when communicating are12of the effort.
    Butterflies. Of course. I rushed to13them from the garbage,14them off and handed them to my young artist. “Want to see them15again?” he asked with a shy smile. “Oh yes! They're beautiful.” I whispered. He ran back upstairs to float his16 down again. They really did look like beautiful butterflies.
    That day Paul 17me to look up at 18instead of down at garbage. How many other masterpieces (杰作) do I miss because I'm too caught up in my 19to take time to appreciate what's right in front of me? Life is not what happens to us. It's 20 we look at it. Now, I look up.