读课文《旅鼠之谜》，“是的，这就是神秘莫测的北极旅鼠，人们研究了好几个世纪，却始终解不开它们的奥秘”，划线词语说明了什么？

    I started to learn English when I was six. My dad gave me1advice on listening to the Beatles. I listened to them every day for the next seven years. At the beginning, I could understand2of what they sang. But soon I started to understand some of the3.

    4 I got a book with the words of all the songs. And when I had time, I would read it. I learned many songs5this book. I6the songs to myself. Still, I understood very7of the meaning. To learn English well became my8, and I wanted to learn the9of the Beatles' songs. That is how I started to learn English.

    Today, I can understand the Beatles very10. Each time I hear a Beatles' song, I am happy and proud because my dream of learning English well has come true.

央视315指广药维C银翘片含剧毒砷、汞残留，其中这里的砷、汞是指____（填“原子”“单质”或“元素”）．

2007年8月31日，党和国家领导人***、温家宝、曾庆红、李长春在北京中南海怀仁堂亲切会见全国优秀教师代表。这说明（      ）

①尊师重教是中华民族的传统美德
②我国党和政府十分重视教育事业
③教师的地位太低，借此抬高老师的地位
④尊师重教是一个社会文明的标志