黔东南某中学历史兴趣小组进行课题研究，列出的关键词是“黄河流域、半地穴式房屋、 粟”，请你判断他们研究的是哪一原始人群(　　)

如图是根尖结构示意图，请填写出各结构的名称，并回答问题（在中填编号）

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阅读下面短文，掌握其大意，然后从1—20各题所给的四个选项（A、B、C和D）中，选出最佳选项。

    I was required to read one of Bernie Siegel's books in college and was hooked on his positivity from that moment on．The stories of his unconventional1 and the exceptional patients he wrote about were so2 to me and had such a big3 on how I saw life from then on．

    Who knew that so many years later I would look to Dr．Bernie and his CDs again to4 my own Cancer experience ？

    I'm an ambitious5 , and when I started going through chemo( 化疗 )，even though I'm a very6 person, I lost my drive to write．I was just too tired and not in the7 ．One day, while waiting to go in for 8, I had one of Dr．Bernie's books in hand．Another patient 9 what I was reading and struck up a conversation with me10 he had one of his books with me as well．It11that among other things, he was an eighty-year-old writer．He was12a published author, and he was currently13on a new book．

    We would see each other at various times and14friends．Sometimes he wore a duck hat, and I would  tell myself, he was definitely a ( n ) 15 of Dr．Berline．He really put a16 on my face．He unfortunately17last year due to his cancer,18 he left a deep impression on me and gave me the19 to pick up my pen again．I20 to myself, “If he can do it, then so can I．”